EP0949317B1 - Process for the isomerisation of gasolines with high benzene content - Google Patents

Process for the isomerisation of gasolines with high benzene content Download PDF

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Publication number
EP0949317B1
EP0949317B1 EP99400568A EP99400568A EP0949317B1 EP 0949317 B1 EP0949317 B1 EP 0949317B1 EP 99400568 A EP99400568 A EP 99400568A EP 99400568 A EP99400568 A EP 99400568A EP 0949317 B1 EP0949317 B1 EP 0949317B1
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Prior art keywords
fluid
reactor
make
process according
isomerization
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German (de)
French (fr)
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EP0949317A1 (en
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Marc Fersing
Pedro Nascimento
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Total Marketing Services SA
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TotalFinaElf France SA
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    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G45/00—Refining of hydrocarbon oils using hydrogen or hydrogen-generating compounds
    • C10G45/58—Refining of hydrocarbon oils using hydrogen or hydrogen-generating compounds to change the structural skeleton of some of the hydrocarbon content without cracking the other hydrocarbons present, e.g. lowering pour point; Selective hydrocracking of normal paraffins
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G2400/00—Products obtained by processes covered by groups C10G9/00 - C10G69/14
    • C10G2400/02—Gasoline

Definitions

  • the present invention relates to an improved method for the isomerization of gasoline with a high benzene content.
  • gasoline isomerization processes which aim to increase the octane number of these species by transformation of linear paraffins which contain branched paraffins (or isoparaffins).
  • the load to be treated is mainly composed of saturated hydrocarbons with five or six carbon atoms, as well as lower proportions of hydrocarbons to four or seven carbon atoms, and benzene which like everyone knows is relatively difficult to separate from other hydrocarbons with six carbon atoms.
  • the charge to be treated is most often mixed with hydrogen and to a possible recycle, then directed to at least one reactor containing a suitable catalyst in a fixed bed.
  • the temperature prevailing in this reactor is usually between 120 and 190 ° C.
  • effluents are routed to one or more separation columns. Often times isoparaffins are then separated from non-paraffins isomerized: the first are sent in principle to the essences pool, to serve as bases for the formulation of fuels, while the seconds are eventually recycled to the reactor, to be transformed there.
  • the first reactor in which product, in addition to the isomerization of paraffins, the hydrogenation of traces of benzene present in the load, operates at slightly higher temperature than the second, where the isomerization reaction ends proper. Indeed, from a kinetic point of view, the paraffin isomerization reaction is slower than the benzene hydrogenation reaction. In addition, the lower temperature prevailing in the second reactor is thermodynamically favorable for product formation branched trees sought.
  • the benzene content of the fillers isomerization remains relatively limited. Indeed, a commonly accepted rule considers that an increase in the benzene content of 1% in the feed to be treated a 10 ° C rise in temperature within the first isomerization reactor. Knowing that other reactions that the hydrogenation of benzene already produce to them only a temperature rise of around 15 ° C, the benzene content of the feedstock entering this reactor must then be limited to 4%. Beyond this content, the temperature in the reactor is too high, which ultimately damages not only the catalyst but also the unit, designed to operate at room temperature limited. Furthermore, at high temperature, reactions unwanted side effects occur, such as, by example, hydrocracking reactions of the charge.
  • An ingenious solution then consists in admitting in the isomerization unit, in addition to the conventional charges, cuts of benzene-rich gasolines, such as some fuel cuts from reforming units or catalytic cracking: the benzene present in these cuts is thus hydrogenated in the isomerization unit, and this ultimately reduces the content of benzene of the said cuts before sending them to the "pool essences ", term by which we designate all the bases used to make petroleum products.
  • the patent US N ° 5,003,118 proposes to introduce, upstream of the isomerization reactors themselves, a charge pretreatment, specifically intended for perform the hydrogenation of the benzene present in this charge. In this way, the unit is able to deal with fillers with higher benzene content.
  • This solution has the disadvantage of being of high cost, linked to the necessary construction of additional equipment. Besides, it is absolutely not flexible, insofar as the hydrogenation reactor is of no useful in the case of a load with a low benzene content.
  • the present invention therefore aims to propose a method isomerization of gasoline with a high benzene content, allowing a simple and inexpensive remedy to problems encountered in the prior art.
  • the present invention also aims to provide a particularly flexible isomerization process, allowing to adapt quickly to different charges intended for him.
  • the subject of the present invention is a process for the isomerization of a hydrocarbon feed containing a substantial amount of paraffinic hydrocarbons with 5 or 6 carbon atoms and of benzene at a content greater than or equal to 2% by weight, in which the charge to be treated passes, in the presence of hydrogen, to a total pressure greater than or equal to 10 ⁇ 10 5 Pa (10 bars) and to an average temperature between 100 and 200 ° C., in at least one reactor containing a catalyst of isomerization of paraffinic hydrocarbons, this process being characterized in that one introduces, in the upstream part of the reaction zone, a make-up fluid which, at 40 ° C and under atmospheric pressure (1.0134.10 5 Pa ), is in the gaseous state and has a density less than or equal to that of normal-pentane considered under the same conditions, this make-up fluid comprising at least 98% by weight of hydrocarbons comprising from one to four ato carbon.
  • density of a gaseous fluid is meant the ratio between the density of this fluid and the density dry air with normal carbon dioxide content, these two densities being measured in the same temperature and pressure conditions.
  • the density of the make-up fluid will be measured, at 40 ° C and under a pressure of 1.0134.10 5 Pa (1 atmosphere), by applying to any of the fluids any of the standardized measurement methods described in standard ASTM D1070-85 (R94). The same is true for normal-pentane.
  • the densities of said makeup fluid and of pentane will be considered by reference to the same measurement method.
  • the makeup fluid is in the gaseous state at 40 ° C under a pressure of 1.0134.10 5 Pa (1 atmosphere).
  • it is introduced into the upstream part of the reaction zone under conditions of temperature and pressure directly dependent on the operating conditions of the process. Depending on its composition, it can then be in the liquid or gaseous state or in an intermediate state.
  • the preferred hydrocarbons in the make-up fluid are methane and ethane.
  • This fluid can thus, for example, be made of natural gas.
  • This fluid can also comprise, in quantity minority, hydrocarbons with six or seven atoms of carbon, and / or inert gases such as nitrogen, or any other suitable light fluid.
  • said makeup fluid contains a substantial amount of light compounds from a fractionation column located downstream of the isomerization unit.
  • This drop in temperature therefore depends only on the following parameters: flow rates and load compositions and make-up fluid, pressure, temperature, fraction vaporized charge at the reactor inlet and report mass between hydrogen and charge in the mixture reaction allowed in the unit. So it can be perfectly controlled and optimized according to the benzene content of the feed to be isomerized.
  • the process according to the invention is precise and extremely flexible, since the flow of the makeup fluid can be adjusted to compensate exactly the temperature rise due to the content of benzene higher than the generally accepted maximum level.
  • the method according to the invention proves to be very advantageous for units which do not have, downstream of the isomerization unit, a deisohexanizer (column of separation of the branched paraffins sought and the linear paraffins), with recycle of a cut rich in linear paraffins upstream of the isomerization unit.
  • One of the goals of this recycling is to dilute the fresh load allowed in the unit, in order to lower the benzene content. Thanks to the invention, since it is it is possible to admit more content to the unit high in benzene, this dilution is no longer necessary.
  • the method according to the invention therefore represents a very valid alternative to the costly installation of a deisohexanizer and a system of recycle.
  • the process according to the invention has been found to provide increased recovery light hydrocarbons containing not more than four atoms of carbon, and in particular propane and butane.
  • LPG Petroleum Gas Liquefied
  • the isomerization unit can be so operated with a view to increased production of these LPGs.
  • the make-up fluid is injected into the upstream part of the reaction zone. This means that said fluid can be injected into the part upstream of the first reactor proper, and / or immediately upstream of the latter.
  • make-up fluid is injected in the upstream part of the first isomerization reactor, at know in the area extending from the level of introduction into the reaction mixture reactor (feed and hydrogen) halfway up the catalytic bed.
  • Make-up fluid can then be injected into the reactor area included between the introduction of the reaction mixture and the start of the dense bed of catalyst.
  • fluid can also be injected directly into the dense bed of catalyst, in the first half of this latest.
  • make-up fluid When make-up fluid is injected immediately in upstream of the first reactor, it is introduced immediately before the introduction of the reaction mixture (charge and hydrogen) in the first reactor, i.e. after complete preheating of this mixture and before injection of this in the first reactor.
  • This injection of makeup fluid has a purely thermal and therefore has nothing to do with the injection, in large quantities, of the hydrogen necessary for the actual isomerization reaction, which takes place, in a manner known per se, upstream of the unit isomerization, i.e. upstream of the heat exchangers heat in which the reaction mixture (charge and hydrogen) is heated before being introduced into the reactor.
  • make-up fluid is therefore carried out, moreover, compared to the usual injection of hydrogen in upstream of the unit, in a completely different location, and with a much lower volume flow.
  • this make-up fluid which has a purely thermal effect, can consist of any gas light compatible with the process, while hydrogen introduced upstream of the isomerization unit has an effect chemical at the level of the actual reaction.
  • This make-up fluid is advantageously injected at a rate of 5 to 150 Nm 3 per m 3 of charge to be isomerized and, preferably, from 5 to 60 Nm 3 per m 3 of charge.
  • the starting charge is considered here, before mixing with hydrogen and heating of the reaction mixture thus obtained.
  • the make-up fluid either injected at a temperature below or above that of the reaction medium. That said, it is better inject said fluid at a lower temperature or equal to that of the reaction medium and, preferably, between 20 and 180 ° C.
  • a particularly variant advantageous of the invention consists in recycling, immediately downstream of the first reactor, a rich section into slightly branched paraffins with 5 or 6 carbon atoms and which usually contains naphthenes. This cut comes, in a manner known per se, from a fractionation existing in advanced isomerization units, which is located downstream of the reactors, and which separates the isoparaffins sought from other compounds.
  • this recycle cut which does not contains no benzene, is traditionally introduced upstream of the first reactor, in order not only to perform an additional passage in the isomerization unit, but also to dilute the fresh charge allowed in the unit, to so as to lower the benzene content of the charge combined thus obtained.
  • a make-up fluid supply line can open in the finish line at the first reactor of the mixture reaction (charge and hydrogen), between the warming up the most downstream reaction mixture and injection point of said mixture in the first reactor.
  • the make-up fluid When the make-up fluid is introduced into the breast of the first reactor, at least one means of introducing make-up fluid flows into this reactor, upstream of the bed dense catalyst and / or within the first half of this last.
  • the one or more means can then be constituted by any known means allowing, downstream of the injection of the charge itself, the introduction of a light fluid in a reactor.
  • a cane or even a single tube with side slits or more orifices, to allow better distribution of the make-up fluid.
  • a diffuser is used allowing to introduce the make-up fluid so homogeneous over the entire section of the reactor.
  • said means for introducing make-up fluid can lead into the reactor in multiple ways.
  • said means open out transversely in the reactor, substantially perpendicular to the axis of the latter.
  • At least one means of introduction of make-up fluid opens into the reactor substantially parallel to the axis of the latter.
  • said means then enters the reactor by the orifice allowing the introduction of the reaction mixture.
  • the invention does not relate to catalysts capable of to intervene in its implementation.
  • We can, in fact, employ any known catalyst exhibiting activity for isomerization of linear paraffins into paraffins branched.
  • many catalysts are known to those skilled in the art. They usually have a or more acidic functions, as well as a function hydrogenating (hydrogenating transition metal).
  • FIG. 1 represents a unit for the isomerization of sections containing linear paraffins with 5 or 6 atoms of carbon.
  • This charge arrives via line 1, in which hydrogen and possibly recycle gases are introduced by line 2.
  • the reaction mixture thus obtained is routed by line 33 to two heat exchangers heat 3 and 4, against the effluent from both unit isomerization reactors.
  • the reaction mixture thus reheated is then introduced into a first reactor 5, or upstream reactor.
  • the latter contains a isomerization catalyst distributed in a catalytic bed 6, which occupies most of the height of the reactor 5.
  • the effluent from the latter, after passing through the exchanger 4 is then introduced via line 7 into the second reactor 8, or downstream reactor, which is also loaded with an isomerization catalyst distributed in a catalytic bed 9.
  • the load to be treated flows from high down in reactors 5 and 8, but it could naturally circulate there from bottom to top.
  • the device further includes valve systems, not represented, allowing to interrupt independently feeding reactors 5 and 8 and / or reversing the direction circulation of the reaction mixture.
  • a make-up fluid is injected into the upstream reactor 5, via a rod 11 substantially perpendicular to the axis of the reactor and which leads directly into the catalytic bed, into the first half of it.
  • This rod is provided with side slits, not shown, allowing better distribution.
  • the catalytic bed 6 of the upstream reactor 5 can be separated into an upstream section 12 and a downstream section 13, which contain the same isomerization catalyst.
  • the rod 11 a for introducing make-up fluid then enters the reactor between the two catalytic sections 12 and 13.
  • a stepped injection system 11b allows the introduction of make-up fluid at several levels in the first half of the catalytic bed 6 of the reactor 5.
  • an injection system 11 c of make-up fluid opens into the reactor 5 in a manner substantially parallel to the axis of the latter, at the orifice allowing the introduction of the reaction mixture (feed and hydrogen) supplied to the reactor via line 33.
  • a line 11 d for supplying make-up fluid opens into the inlet line 33 of the reaction mixture (feed and hydrogen), immediately upstream of the first reactor. isomerization 5.
  • FIG. 6 shows how the invention can allow improve the relationships between the unit isomerization and other petroleum units.
  • the fraction rich in isopentane which is a compound with high octane number therefore requiring no treatment isomerization, is evacuated via line 19.
  • Light petrol depleted in isopentane then crosses the two reactors isomerization 5 and 8 as described above, and the load enriched in isoparaffins is extracted therefrom by line 10.
  • This charge is then separated, within the stabilizer 20, in a head section 21, consisting of compounds with up to four carbon atoms, and a cut background 22 of heavier compounds .: The latter is then directed to the deisohexanizer 23, where it found divided into an isomerate 26, consisting of isoparaffins with 5 or 6 carbon atoms, and a heavy cut 25, essentially consisting of naphthenes and paraffins at 7 carbon atoms or more.
  • the essence heavy discharged from separator 15 via line 17 is directed towards the reforming unit 27, within which it undergoes among others aromatization reactions, which contribute to increase its content of aromatic products, including benzene.
  • the reformate thus produced is then separated at level of fractionation 28 into a heavy reformate 29, the boiling point is above about 90 ° C, which is routed to the gasoline pool, and a light reformate 31, whose boiling point is between about 30 ° C and 90 ° C.
  • a means 11 for injecting a make-up fluid enters the catalytic bed of the upstream reactor 5.
  • the make-up fluid consists of compounds comprising at most 4 carbon atoms derived from the line 35 of the head cup, discharged at 21, from stabilizer 20.
  • the isomerization unit is likely to deal with charges with content higher in benzene than in the prior art. So the Doubling the amount of benzene present in the charge can be thermally compensated by adding fluid light (density less than or equal to that of normal-pentane), the flow rate of which will be adjusted according to the benzene content of the feed to be isomerized.
  • the purpose of this example is to illustrate the limits of conventional gasoline isomerization processes, in the case treatment of loads with high benzene content.
  • This charge is combined with a gaseous mixture rich in hydrogen (20% by weight of hydrogen), introduced at a flow rate of 2 t / h.
  • This reaction mixture is then warmed up to 133 ° C., then treated in a conventional gasoline isomerization unit comprising two reactors in series, operating at a pressure of 31 ⁇ 10 5 Pa.
  • the temperature recorded at the outlet of the first reactor is 180 ° C.
  • this charge No. 2 has a content of benzene of 7.66% by weight and a density at 15 ° C of 0.687. The other properties remain globally unchanged by in relation to charge # 1.
  • This charge n ° 2 is treated under the same conditions than those mentioned above for the treatment of charge # 1, except gas flow rich in hydrogen, which is brought to 3.5 t / h (so known per se, the isomerization of charges rich in benzene requires an increased amount of hydrogen in the medium reactive, taking into account the additional consumption hydrogen induced by the hydrogenation of benzene).
  • the temperature recorded at the outlet of the first reactor is then 193 ° C. So there was an increase in temperature of 13 ° C in this reactor, due to the high quantity of heat given off by the hydrogenation of the supplement benzene present in charge # 2. Ultimately, this temperature increase in the first reactor risk not only damage the catalyst and the unit, but also to decrease the reaction yields isomerization (better at low temperature).
  • charge rich in benzene described above (charge n ° 2) is treated this time according to the isomerization process according to the invention.
  • a fluid make-up is therefore introduced into the catalytic bed of the first reactor, at the level of the first third of the bed catalytic (exactly 2/7 of this bed), and with a flow of 30Nm3 per m3 of load.
  • Two introduction temperatures make-up fluid have been tested: 30 ° C (temperature lower than that of the reaction medium) and 145 ° C. (temperature of the order of that of the reaction medium).
  • Fluid Composition (in% by weight) Density (40 ° C, 1.0134 Pa) F1 2% H 2 + 12% CH 4 + 18% C 2 H 6 + 25% C 3 H 8 + 43% C 4 H 10 1.04.10 -3 F2 2% H 2 + 80% CH 4 + 16% C 2 H 6 + 2% C 3 H 3 0.59.10 -3 F4 100% CH 4 0.62.10 -3 F5 100% C 2 H 6 1.16.10 -3 F6 100% C 3 H 8 1.72.10 -3 F7 100% nC 4 H 10 2.28.10 -3
  • the fluid F1 corresponds to a gaseous mixture of the type of those that can recover at the head of a column of fractionation located downstream of the isomerization unit (so-called stabilization column).
  • the operating conditions are identical to those described in Example 1 for the treatment of the charge n ° 2, and the inlet temperature of the reaction mixture in the first isomerization reactor is notably maintained at 133 ° C.
  • Test 1 corresponds to a zero makeup fluid flow rate (prior art).
  • Trial Fluid flow extra (Nm 3 per m 3 of charge)
  • Temperature release of the first reactor (° C) 1 0 193 2 10 188 3 30 181 4 60 173
  • This example illustrates the excellent thermal control to which the invention gives access.
  • This control is extremely precise and flexible, since the fluid flow can be optimized according to the characteristics the load to be treated and, in particular, its content benzene.
  • This example specifies the conditions in which the process according to the invention must be implemented work, and in particular the nature of the make-up fluids likely to be employed.
  • thermodynamic effect described is not produces more and the injection of make-up fluid does not allow more to lower the temperature of the first reactor.
  • the thermodynamic effect described is not produces more and the injection of make-up fluid does not allow more to lower the temperature of the first reactor.

Abstract

Upstream of the reactor a balance fluid is introduced, which, at 40 degrees C and atmospheric pressure, is a gas and has a density less than or equal to that of pentane under the same conditions. The paraffins have 5 or 6 atoms and more than 2 wt.% benzene, in which the load is passed through a reactor (5) containing an isomerization catalyst in the presence of hydrogen, at a total pressure greater than 10 x 10<5> Pa (10 bars) and a mean temperature of 100-200 degrees C. The balance fluid is injected immediately upstream of the first isomerization reactor, at a level in the introduction zone where the fluids are mixed, at mid- height of the catalyst bed (6), and after preheating of the reaction mixture and before injecting the mixture into the reactor. The balance fluid contains a substantial quantity of hydrogen and/or hydrocarbons with 1-5 (or 1-4) C. The fluid also contains a small quantity of hydrocarbons with 6 or 7 C and/or inert gases such as nitrogen or other appropriate light fluid. The fluid contains a substantial quantity of the light components from a fractionating column (20) for the effluents from the isomerization unit. The composition and/or flow rate of the balance fluid is optimized as a function of the characteristics of the load to be treated, in particular its benzene content. The balance fluid is injected at a rate of 5-150 Nm<3>/m<3> of load, preferably 5-60 Nm<3>/m<3> of load, and at a temperature less than or equal to that of the reactants, preferably 20-180 degrees C. The isomerization unit contains several reactors in series (5, 8) and a section rich in non-isomerized paraffins with 5 or 6 C containing naphthenes, is separated from the effluent of the isomerization unit and is recycled immediately downstream of the first reactor. Independent claims are included for: (i) the apparatus for the above process; and (ii) the use of the unit to isomerize light petrols from catalytic cracking, on their own or part of a mixture.

Description

La présente invention concerne un procédé amélioré pour l'isomérisation d'essences à teneur élevée en benzène.The present invention relates to an improved method for the isomerization of gasoline with a high benzene content.

De manière connue en soi, l'industrie pétrolière a recours à des procédés dits d'isomérisation des essences, qui visent à augmenter l'indice d'octane de ces essences par transformation des paraffines linéaires quelles contiennent en paraffines ramifiées (ou isoparaffines). En général, la charge à traiter est majoritairement, composée d'hydrocarbures saturés à cinq ou six atomes de carbone, ainsi que de plus faibles proportions d'hydrocarbures à quatre ou sept atomes de carbone, et de benzène qui, comme chacun sait, est relativement difficile à séparer des autres hydrocarbures à six atomes de carbone.In known manner, the petroleum industry has use of so-called gasoline isomerization processes, which aim to increase the octane number of these species by transformation of linear paraffins which contain branched paraffins (or isoparaffins). In general, the load to be treated is mainly composed of saturated hydrocarbons with five or six carbon atoms, as well as lower proportions of hydrocarbons to four or seven carbon atoms, and benzene which like everyone knows is relatively difficult to separate from other hydrocarbons with six carbon atoms.

Pour effectuer la réaction d'isomérisation, la charge à traiter est le plus souvent mélangée à de l'hydrogène et à un éventuel recycle, puis dirigée vers au moins un réacteur contenant un catalyseur approprié en lit fixe. La température régnant dans ce réacteur est usuellement comprise entre 120 et 190°C. A la sortie du (ou des) réacteur(s) d'isomérisation, les effluents sont acheminés vers une ou plusieurs colonnes de séparation. Souvent, les isoparaffines sont alors séparées des paraffines non isomérisées : les premières sont envoyées en principe au pool essences, pour servir de bases pour la formulation des carburants, tandis que les secondes sont éventuellement recyclées au réacteur, afin d'y être transformées.To carry out the isomerization reaction, the charge to be treated is most often mixed with hydrogen and to a possible recycle, then directed to at least one reactor containing a suitable catalyst in a fixed bed. The temperature prevailing in this reactor is usually between 120 and 190 ° C. On leaving (or) isomerization reactor (s), effluents are routed to one or more separation columns. Often times isoparaffins are then separated from non-paraffins isomerized: the first are sent in principle to the essences pool, to serve as bases for the formulation of fuels, while the seconds are eventually recycled to the reactor, to be transformed there.

On sait également que, dans les conditions de la réaction d'isomérisation, le benzène présent dans la charge est hydrogéné, du fait de la présence de l'hydrogène et des métaux de transition hydrogénants entrant dans la composition des catalyseurs d'isomérisation. Il en résulte, dans la partie amont du réacteur d'isomérisation, un dégagement de chaleur important dû à l'exothermicité de cette réaction, ce qui nuit à l'efficacité de la réaction d'isomérisation.We also know that, under the conditions of the isomerization reaction, the benzene present in the feed is hydrogenated, due to the presence of hydrogen and hydrogenating transition metals entering the composition of the isomerization catalysts. As a result, in the upstream part of the isomerization reactor, a significant heat release due to the exothermicity of this reaction, which affects the effectiveness of the reaction isomerization.

C'est pourquoi on opère usuellement avec deux réacteurs d'isomérisation: le premier réacteur, dans lequel se produit, en plus de l'isomérisation des paraffines, l'hydrogénation des traces de benzène présentes dans la charge, fonctionne à température légèrement plus élevée que le second, où se termine la réaction d'isomérisation proprement dite. En effet, d'un point de vue cinétique, la réaction d'isomérisation des paraffines est plus lente que la réaction d'hydrogénation du benzène. De plus, la température plus basse régnant dans le second réacteur est thermodynamiquement favorable à la formation des produits ramifiés recherchés.This is why we usually operate with two reactors isomerization: the first reactor, in which product, in addition to the isomerization of paraffins, the hydrogenation of traces of benzene present in the load, operates at slightly higher temperature than the second, where the isomerization reaction ends proper. Indeed, from a kinetic point of view, the paraffin isomerization reaction is slower than the benzene hydrogenation reaction. In addition, the lower temperature prevailing in the second reactor is thermodynamically favorable for product formation branched trees sought.

Cependant, la teneur en benzène des charges d'isomérisation reste relativement limitée. En effet, une règle communément admise considère qu'une augmentation de la teneur en benzène de 1% dans la charge à traiter entraíne une élévation de température de 10°C au sein du premier réacteur d'isomérisation. Sachant que les réactions autres que l'hydrogénation du benzène produisent déjà à elles seules une élévation de température de l'ordre de 15°C, la teneur en benzène de la charge pénétrant dans ce réacteur doit être alors limitée à 4%. Au delà de cette teneur, la température régnant dans le réacteur est trop élevée, ce qui, à terme, endommage non seulement le catalyseur mais également l'unité, conçue pour fonctionner à température limitée. Par ailleurs, à température élevée, des réactions secondaires indésirables se produisent, telles que, par exemple, des réactions d'hydrocraquage de la charge.However, the benzene content of the fillers isomerization remains relatively limited. Indeed, a commonly accepted rule considers that an increase in the benzene content of 1% in the feed to be treated a 10 ° C rise in temperature within the first isomerization reactor. Knowing that other reactions that the hydrogenation of benzene already produce to them only a temperature rise of around 15 ° C, the benzene content of the feedstock entering this reactor must then be limited to 4%. Beyond this content, the the temperature in the reactor is too high, which ultimately damages not only the catalyst but also the unit, designed to operate at room temperature limited. Furthermore, at high temperature, reactions unwanted side effects occur, such as, by example, hydrocracking reactions of the charge.

Toutefois, il apparaít désirable de pouvoir traiter dans l'unité d'isomérisation des charges à teneur en benzène beaucoup plus élevée que les 4% généralement admis.However, it appears desirable to be able to deal with the benzene content charge isomerization unit much higher than the generally accepted 4%.

En effet, compte tenu du caractère cancérigène du benzène, les normes actuelles tendent à imposer des limitations de plus en plus draconiennes de la teneur de ce composé dans les carburants.Indeed, given the carcinogenic nature of benzene, current standards tend to impose increasingly draconian limitations of the content of this compound in fuels.

Une solution ingénieuse consiste alors à admettre dans l'unité d'isomérisation, en plus des charges classiques, des coupes d'essences riches en benzène, telles que certaines coupes d'essences issues des unités de réformage ou de craquage catalytique : le benzène présent dans ces coupes est ainsi hydrogéné dans l'unité d'isomérisation, et cette opération permet in fine de réduire nettement la teneur en benzène desdites coupes avant de les acheminer au "pool essences", terme par lequel on désigne l'ensemble des bases utilisées pour fabriquer des produits pétroliers.An ingenious solution then consists in admitting in the isomerization unit, in addition to the conventional charges, cuts of benzene-rich gasolines, such as some fuel cuts from reforming units or catalytic cracking: the benzene present in these cuts is thus hydrogenated in the isomerization unit, and this ultimately reduces the content of benzene of the said cuts before sending them to the "pool essences ", term by which we designate all the bases used to make petroleum products.

Ce besoin de traiter plus de benzène à l'isomérisation se heurte cependant à la contrainte liée à la température régnant dans le premier réacteur. Il demeure en effet indispensable de maintenir cette température à une valeur moyenne de l'ordre de 180°C, température au-delà de laquelle commencent les réactions d'hydrocraquage, qui sont très exothermiques.This need to process more benzene to isomerization however, faces the temperature constraint prevailing in the first reactor. It remains indeed essential to maintain this temperature at a value average of around 180 ° C, temperature above which start the hydrocracking reactions, which are very exothermic.

Afin de s'affranchir de cette limitation, le brevet US N° 5 003 118 propose d'introduire, en amont du ou des réacteurs d'isomérisation proprement dits, un réacteur de prétraitement de la charge, spécifiquement destiné à réaliser l'hydrogénation du benzène présent dans cette charge. De la sorte, l'unité est à même de traiter des charges à teneur en benzène plus élevée. Cette solution présente cependant le désavantage d'être d'un coût élevé, lié à la nécessaire construction d'équipements supplémentaires. En outre, elle n'est absolument pas flexible, dans la mesure où le réacteur d'hydrogénation n'est d'aucune utilité dans le cas d'une charge à faible teneur en benzène.In order to overcome this limitation, the patent US N ° 5,003,118 proposes to introduce, upstream of the isomerization reactors themselves, a charge pretreatment, specifically intended for perform the hydrogenation of the benzene present in this charge. In this way, the unit is able to deal with fillers with higher benzene content. This solution has the disadvantage of being of high cost, linked to the necessary construction of additional equipment. Besides, it is absolutely not flexible, insofar as the hydrogenation reactor is of no useful in the case of a load with a low benzene content.

La présente invention vise donc à proposer un procédé d'isomérisation d'essences à teneur élevée en benzène, permettant de remédier de façon simple et peu coûteuse aux problèmes rencontrés dans l'art antérieur.The present invention therefore aims to propose a method isomerization of gasoline with a high benzene content, allowing a simple and inexpensive remedy to problems encountered in the prior art.

La présente invention vise également à proposer un procédé d'isomérisation particulièrement flexible, permettant de s'adapter de manière rapide aux différentes charges qui lui sont destinées.The present invention also aims to provide a particularly flexible isomerization process, allowing to adapt quickly to different charges intended for him.

A cet effet, la présente invention a pour objet un procédé d'isomérisation d'une charge hydrocarbonée contenant une quantité substantielle d'hydrocarbures paraffiniques à 5 ou 6 atomes de carbone et du benzène à une teneur supérieure ou égale à 2% en poids, dans lequel la charge à traiter passe, en présence d'hydrogène, à une pression totale supérieure ou égale à 10.105 Pa (10 bars) et à une température moyenne comprise entre 100 et 200°C, dans au moins un réacteur contenant un catalyseur d'isomérisation d'hydrocarbures paraffiniques, ce procédé étant caractérisé en ce que l'on introduit, dans la partie amont de la zone réactionnelle, un fluide d'appoint qui, à 40°C et sous pression atmosphérique (1,0134.105 Pa), se trouve à l'état gazeux et possède une densité inférieure ou égale à celle du normal-pentane considéré dans les mêmes conditions, ce fluide d'appoint comprenant au moins 98 % en poids d'hydrocarbures comportant de un à quatre atomes de carbone.To this end, the subject of the present invention is a process for the isomerization of a hydrocarbon feed containing a substantial amount of paraffinic hydrocarbons with 5 or 6 carbon atoms and of benzene at a content greater than or equal to 2% by weight, in which the charge to be treated passes, in the presence of hydrogen, to a total pressure greater than or equal to 10 × 10 5 Pa (10 bars) and to an average temperature between 100 and 200 ° C., in at least one reactor containing a catalyst of isomerization of paraffinic hydrocarbons, this process being characterized in that one introduces, in the upstream part of the reaction zone, a make-up fluid which, at 40 ° C and under atmospheric pressure (1.0134.10 5 Pa ), is in the gaseous state and has a density less than or equal to that of normal-pentane considered under the same conditions, this make-up fluid comprising at least 98% by weight of hydrocarbons comprising from one to four ato carbon.

Par densité d'un fluide gazeux, on entend le rapport entre la masse volumique de ce fluide et la masse volumique de l'air sec et à teneur normale en dioxide de carbone, ces deux masses volumiques étant mesurées dans les mêmes conditions de température et de pression.By density of a gaseous fluid is meant the ratio between the density of this fluid and the density dry air with normal carbon dioxide content, these two densities being measured in the same temperature and pressure conditions.

La densité du fluide d'appoint sera mesurée, a 40°C et sous une pression de 1,0134.105 Pa (1 atmosphère), en appliquant audit fluide l'une quelconque des méthodes de mesure normalisées décrites dans la norme ASTM D1070-85 (R94). Il en est de même pour le normal-pentane. Les densités dudit fluide d'appoint et du pentane seront considérées par référence à la même méthode de mesure.The density of the make-up fluid will be measured, at 40 ° C and under a pressure of 1.0134.10 5 Pa (1 atmosphere), by applying to any of the fluids any of the standardized measurement methods described in standard ASTM D1070-85 (R94). The same is true for normal-pentane. The densities of said makeup fluid and of pentane will be considered by reference to the same measurement method.

Selon l'invention, le fluide d'appoint se trouve à l'état gazeux à 40°C sous une pression de 1,0134.105 Pa (1 atmosphère). Par contre, il est introduit dans la partie amont de la zone réactionnelle dans des conditions de température et de pression dépendant directement des conditions opératoires du procédé. Selon sa composition, il peut alors se trouver à l'état liquide ou gazeux ou dans un état intermédiaire. According to the invention, the makeup fluid is in the gaseous state at 40 ° C under a pressure of 1.0134.10 5 Pa (1 atmosphere). On the other hand, it is introduced into the upstream part of the reaction zone under conditions of temperature and pressure directly dependent on the operating conditions of the process. Depending on its composition, it can then be in the liquid or gaseous state or in an intermediate state.

Les hydrocarbures préférés du fluide d'appoint sont le méthane et l'éthane. Ce fluide peut ainsi, par exemple, être constitué de gaz naturel.The preferred hydrocarbons in the make-up fluid are methane and ethane. This fluid can thus, for example, be made of natural gas.

Ce fluide peut également comprendre, en quantité minoritaire, des hydrocarbures à six ou sept atomes de carbone, et/ou des gaz inertes tels que de l'azote, ou tout autre fluide léger approprié.This fluid can also comprise, in quantity minority, hydrocarbons with six or seven atoms of carbon, and / or inert gases such as nitrogen, or any other suitable light fluid.

De manière avantageuse, ledit fluide d'appoint contient une quantité substantielle de composés légers issus d'une colonne de fractionnement située en aval de l'unité d'isomérisation.Advantageously, said makeup fluid contains a substantial amount of light compounds from a fractionation column located downstream of the isomerization unit.

L'introduction de fluide d'appoint léger a pour effet de créer, dans la partie amont de la zone réactionnelle, une vaporisation d'une partie de la fraction liquide de la charge hydrocarbonée. Ce phénomène est endothermique et contribue à rétablir le bilan thermique au sein du réacteur. on peut ainsi compenser l'excès de chaleur qui se dégage dans la partie amont du premier réacteur, à la suite de l'hydrogénation du benzène présent en quantité plus élevée dans la charge.The introduction of light make-up fluid has the effect to create, in the upstream part of the reaction zone, vaporization of part of the liquid fraction of the hydrocarbon feed. This phenomenon is endothermic and helps restore the heat balance within reactor. we can thus compensate for the excess heat which emerges in the upstream part of the first reactor, following of the hydrogenation of the benzene present in more quantity high in load.

En outre, la baisse de température au sein du réacteur, résultant de l'injection dudit fluide, peut être parfaitement déterminée. En effet, cette injection a pour conséquence une modification des équilibres entre les fractions liquide et vapeur des hydrocarbures constitutifs de la charge, équilibres qui sont régis par les lois de la thermodynamique.In addition, the drop in temperature within the reactor, resulting from the injection of said fluid, can be perfectly determined. Indeed, this injection has for consequence a change in the balances between liquid and vapor fractions of the constituent hydrocarbons of load, balances which are governed by the laws of thermodynamic.

Cette baisse de température dépend donc uniquement des paramètres suivants: débits et compositions de la charge et du fluide d'appoint, pression, température, fraction vaporisée de la charge à l'entrée du réacteur et rapport massique entre l'hydrogène et la charge dans le mélange réactionnel admis dans l'unité. Elle peut donc être parfaitement contrôlée et optimisée en fonction de la teneur en benzène de la charge à isomériser. This drop in temperature therefore depends only on the following parameters: flow rates and load compositions and make-up fluid, pressure, temperature, fraction vaporized charge at the reactor inlet and report mass between hydrogen and charge in the mixture reaction allowed in the unit. So it can be perfectly controlled and optimized according to the benzene content of the feed to be isomerized.

De ce fait, le procédé conforme à l'invention est précis et extrêmement flexible, dans la mesure où le débit du fluide d'appoint peut être ajusté de manière à compenser exactement l'élévation de température due à la teneur en benzène supérieure à la teneur maximale généralement admise.Therefore, the process according to the invention is precise and extremely flexible, since the flow of the makeup fluid can be adjusted to compensate exactly the temperature rise due to the content of benzene higher than the generally accepted maximum level.

Grâce au procédé selon l'invention, il devient donc possible d'introduire, en charge de l'unité d'isomérisation, une fraction plus importante d'essences riches en benzène, telles que les essences légères issues du réformage ("réformat léger") et/ou du craquage catalytique, seules ou en mélange avec d'autres charges. Le benzène présent en quantité importante dans ces coupes sera hydrogéné et donc intégralement transformé en composés moins toxiques, au sein de l'unité d'isomérisation. De la sorte, la teneur en benzène de la "coupe essence réduite", constituée de l'isomérat, du réformat léger et du réformat lourd, peut être sensiblement diminuée. L'impact en terme de diminution de la toxicité des carburants est loin d'être négligeable.Thanks to the process according to the invention, it therefore becomes possible to introduce, in charge of the isomerization unit, a larger fraction of benzene-rich essences, such as light essences from reforming ("light reformate") and / or catalytic cracking, alone or mixed with other fillers. Benzene present in significant amount in these cuts will be hydrogenated and therefore completely transformed into less toxic compounds, within of the isomerization unit. In this way, the content of "reduced petrol cut" benzene, consisting of isomerate, light reformate and heavy reformate, can be significantly reduced. The impact in terms of reduction fuel toxicity is far from negligible.

Par ailleurs, le procédé selon l'invention s'avère très avantageux pour les unités ne disposant pas, en aval de l'unité d'isomérisation, d'un déisohexaniseur (colonne de séparation des paraffines ramifiées recherchées et des paraffines linéaires), avec recycle d'une coupe riche en paraffines linéaires en amont de l'unité d'isomérisation.Furthermore, the method according to the invention proves to be very advantageous for units which do not have, downstream of the isomerization unit, a deisohexanizer (column of separation of the branched paraffins sought and the linear paraffins), with recycle of a cut rich in linear paraffins upstream of the isomerization unit.

En effet, un des buts de ce recycle est de diluer la charge fraíche admise dans l'unité, afin d'en abaisser la teneur en benzène. Grâce à l'invention, puisqu'il est possible d'admettre dans l'unité des charges à teneur plus élevée en benzène, cette dilution n'est plus nécessaire.One of the goals of this recycling is to dilute the fresh load allowed in the unit, in order to lower the benzene content. Thanks to the invention, since it is it is possible to admit more content to the unit high in benzene, this dilution is no longer necessary.

Pour de telles unités, le procédé selon l'invention représente donc une alternative très valable à l'installation coûteuse d'un déisohexaniseur et d'un système de recycle.For such units, the method according to the invention therefore represents a very valid alternative to the costly installation of a deisohexanizer and a system of recycle.

Enfin, de manière inattendue, le procédé conforme à l'invention s'est avéré permettre une récupération accrue d'hydrocarbures légers comportant au plus quatre atomes de carbone, et en particulier de propane et de butane. Ces composés sont particulièrement intéressants, d'autant plus qu'ils sont valorisables comme GPL (Gaz de Pétrole Liquéfié), qui est usuellement employé comme carburant ou comme combustible. L'unité d'isomérisation peut être ainsi exploitée dans une optique de production accrue de ces GPL.Finally, unexpectedly, the process according to the invention has been found to provide increased recovery light hydrocarbons containing not more than four atoms of carbon, and in particular propane and butane. These compounds are particularly interesting, especially that they are recoverable as LPG (Petroleum Gas Liquefied), which is usually used as fuel or as fuel. The isomerization unit can be so operated with a view to increased production of these LPGs.

Conformément à l'invention, le fluide d'appoint est injecté dans la partie amont de la zone réactionnelle. Ceci signifie que ledit fluide peut être injecté dans la partie amont du premier réacteur proprement dit, et/ou immédiatement en amont de ce dernier.According to the invention, the make-up fluid is injected into the upstream part of the reaction zone. This means that said fluid can be injected into the part upstream of the first reactor proper, and / or immediately upstream of the latter.

De manière préférée, du fluide d'appoint est injecté dans la partie amont du premier réacteur d'isomérisation, à savoir dans la zone s'étendant du niveau d'introduction dans le réacteur du mélange réactionnel (charge et hydrogène) jusqu'à mi-hauteur du lit catalytique. Du fluide d'appoint peut alors être injecté dans la zone du réacteur comprise entre l'introduction du mélange réactionnel et le début du lit dense de catalyseur. De manière avantageuse, du fluide d'appoint peut également être injecté directement au sein du lit dense de catalyseur, dans la première moitié de ce dernier.Preferably, make-up fluid is injected in the upstream part of the first isomerization reactor, at know in the area extending from the level of introduction into the reaction mixture reactor (feed and hydrogen) halfway up the catalytic bed. Make-up fluid can then be injected into the reactor area included between the introduction of the reaction mixture and the start of the dense bed of catalyst. Advantageously, fluid can also be injected directly into the dense bed of catalyst, in the first half of this latest.

Lorsque du fluide d'appoint est injecté immédiatement en amont du premier réacteur, on l'introduit immédiatement avant l'introduction du mélange réactionnel (charge et hydrogène) dans le premier réacteur, c'est-à-dire apres préchauffage complet de ce mélange et avant injection de celui-ci dans le premier réacteur.When make-up fluid is injected immediately in upstream of the first reactor, it is introduced immediately before the introduction of the reaction mixture (charge and hydrogen) in the first reactor, i.e. after complete preheating of this mixture and before injection of this in the first reactor.

Cette injection de fluide d'appoint a un effet purement thermique et n'a par conséquent rien à voir avec l'injection, en grande quantité, de l'hydrogène nécessaire à la réaction d'isomérisation proprement dite, laquelle s'effectue, de manière connue en soi, en amont de l'unité d'isomérisation, c'est à dire en amont des échangeurs de chaleur dans lesquels le mélange réactionnel (charge et hydrogène) est réchauffé avant d'être introduit dans le réacteur.This injection of makeup fluid has a purely thermal and therefore has nothing to do with the injection, in large quantities, of the hydrogen necessary for the actual isomerization reaction, which takes place, in a manner known per se, upstream of the unit isomerization, i.e. upstream of the heat exchangers heat in which the reaction mixture (charge and hydrogen) is heated before being introduced into the reactor.

Cette injection de fluide d'appoint s'effectue donc, en outre, par rapport à l'injection usuelle d'hydrogène en amont de l'unité, à un endroit totalement différent, et avec un débit volumique beaucoup plus faible. De plus, son rôle est entièrement différent : ce fluide d'appoint, qui a un effet purement thermique, peut être constitué par tout gaz léger compatible avec le procédé, tandis que l'hydrogène introduit en amont de l'unité d'isomérisation a un effet chimique au niveau de la réaction proprement dite.This injection of make-up fluid is therefore carried out, moreover, compared to the usual injection of hydrogen in upstream of the unit, in a completely different location, and with a much lower volume flow. In addition, its role is entirely different: this make-up fluid, which has a purely thermal effect, can consist of any gas light compatible with the process, while hydrogen introduced upstream of the isomerization unit has an effect chemical at the level of the actual reaction.

Ce fluide d'appoint est avantageusement injecté à un débit de 5 à 150 Nm3 par m3 de charge à isomériser et, de préférence, de 5 à 60 Nm3 par m3 de charge. On considère ici la charge de départ, avant mélange avec de l'hydrogène et réchauffement du mélange réactionnel ainsi obtenu.This make-up fluid is advantageously injected at a rate of 5 to 150 Nm 3 per m 3 of charge to be isomerized and, preferably, from 5 to 60 Nm 3 per m 3 of charge. The starting charge is considered here, before mixing with hydrogen and heating of the reaction mixture thus obtained.

L'effet recherché est obtenu, que le fluide d'appoint soit injecté à une température inférieure ou supérieure à celle du milieu réactionnel. Cela dit, il est préférable d'injecter ledit fluide à une température inférieure ou égale à celle du milieu réactionnel et, de préférence, comprise entre 20 et 180°C.The desired effect is obtained, that the make-up fluid either injected at a temperature below or above that of the reaction medium. That said, it is better inject said fluid at a lower temperature or equal to that of the reaction medium and, preferably, between 20 and 180 ° C.

Lorsque l'unité d'isomérisation comprend plusieurs réacteurs en série, une variante particulièrement avantageuse de l'invention consiste à recycler, immédiatement en aval du premier réacteur, une coupe riche en paraffines peu ramifiées à 5 ou 6 atomes de carbone et qui contient généralement des naphtènes. Cette coupe provient, de manière connue en soi, d'un fractionnement existant dans les unités d'isomérisation perfectionnées, qui est situé en aval des réacteurs, et qui sépare les isoparaffines recherchées des autres composés.When the isomerization unit comprises several reactors in series, a particularly variant advantageous of the invention consists in recycling, immediately downstream of the first reactor, a rich section into slightly branched paraffins with 5 or 6 carbon atoms and which usually contains naphthenes. This cut comes, in a manner known per se, from a fractionation existing in advanced isomerization units, which is located downstream of the reactors, and which separates the isoparaffins sought from other compounds.

Dans l'art antérieur, cette coupe de recycle, qui ne contient pas de benzène, est traditionnellement introduite en amont du premier réacteur, afin non seulement d'effectuer un passage supplémentaire dans l'unité d'isomérisation, mais aussi de diluer la charge fraíche admise dans l'unité, de manière à abaisser la teneur en benzène de la charge combinée ainsi obtenue.In the prior art, this recycle cut, which does not contains no benzene, is traditionally introduced upstream of the first reactor, in order not only to perform an additional passage in the isomerization unit, but also to dilute the fresh charge allowed in the unit, to so as to lower the benzene content of the charge combined thus obtained.

Grâce à l'invention, puisqu'il est possible d'admettre dans le premier réacteur des charges à teneur plus élevée en benzène, cette dilution n'est plus nécessaire, de sorte que seule de la charge fraíche est traitée dans le premier réacteur.Thanks to the invention, since it is possible to admit higher content charges in the first reactor in benzene, this dilution is no longer necessary, so that only fresh load is treated in the first reactor.

Il en résulte une bien meilleure valorisation de ce premier réacteur, et une amélioration sensible des réactions d'isomérisation qui s'y produisent. En effet, le débit de charge y est plus faible, ce qui se traduit par une diminution de la vitesse volumique horaire, et donc un temps de contact plus élevé entre la charge et le catalyseur. En outre, recycler cette coupe en aval du premier réacteur permet de ne pas faire circuler dans ce dernier les composés naphténiques, qui sont connus pour être des inhibiteurs des réactions d'isomérisation.This results in a much better valuation of this first reactor, and a significant improvement in isomerization reactions that occur there. Indeed, the charge flow is lower there, which results in a decrease in the hourly space velocity, and therefore a longer contact time between charge and catalyst. In addition, recycle this cut downstream of the first reactor allows not to circulate in this last naphthenic compounds, which are known for be inhibitors of isomerization reactions.

Lorsque le fluide d'appoint est introduit immédiatement en amont du premier réacteur d'isomérisation, une ligne d'alimentation en fluide d'appoint peut déboucher dans la ligne d'arrivée au premier réacteur du mélange réactionnel (charge et hydrogène), entre le dispositif de réchauffement du mélange réactionnel le plus en aval et le point d'injection dudit mélange dans le premier réacteur.When the make-up fluid is introduced immediately upstream of the first isomerization reactor, a make-up fluid supply line can open in the finish line at the first reactor of the mixture reaction (charge and hydrogen), between the warming up the most downstream reaction mixture and injection point of said mixture in the first reactor.

Lorsque le fluide d'appoint est introduit au sein même du premier réacteur, au moins un moyen d'introduction de fluide d'appoint débouche dans ce réacteur, en amont du lit dense de catalyseur et/ou au sein de la première moitié de ce dernier. Le ou lesdits moyens peuvent alors être constitués par tout moyen connu permettant, en aval de l'injection de la charge proprement dite, l'introduction d'un fluide léger dans un réacteur.When the make-up fluid is introduced into the breast of the first reactor, at least one means of introducing make-up fluid flows into this reactor, upstream of the bed dense catalyst and / or within the first half of this last. The one or more means can then be constituted by any known means allowing, downstream of the injection of the charge itself, the introduction of a light fluid in a reactor.

Il peut s'agir par exemple d'une canne (ou même d'un simple tube) pourvue de fentes latérales ou de plusieurs orifices, afin de permettre une meilleure distribution du fluide d'appoint. De préférence, on emploie un diffuseur permettant d'introduire le fluide d'appoint de manière homogène sur toute la section du réacteur.It can be for example a cane (or even a single tube) with side slits or more orifices, to allow better distribution of the make-up fluid. Preferably, a diffuser is used allowing to introduce the make-up fluid so homogeneous over the entire section of the reactor.

Ces moyens d'introduction de fluide d'appoint peuvent déboucher dans le réacteur de multiples manières. Selon un mode de réalisation préféré, lesdits moyens débouchent de manière transversale dans le réacteur, sensiblement perpendiculairement à l'axe de ce dernier.These means for introducing make-up fluid can lead into the reactor in multiple ways. According to a preferred embodiment, said means open out transversely in the reactor, substantially perpendicular to the axis of the latter.

Selon une autre variante, au moins un moyen d'introduction de fluide d'appoint débouche dans le réacteur de manière sensiblement parallèle à l'axe de ce dernier. De préférence, ledit moyen pénètre alors dans le réacteur par l'orifice permettant l'introduction du mélange réactionnel. Cette solution est particulièrement avantageuse dans le cadre de la modernisation d'unités existantes, puisqu'elle évite d'avoir à percer la paroi du réacteur.According to another variant, at least one means of introduction of make-up fluid opens into the reactor substantially parallel to the axis of the latter. Of preferably, said means then enters the reactor by the orifice allowing the introduction of the reaction mixture. This solution is particularly advantageous in the framework of the modernization of existing units, since it avoids having to pierce the reactor wall.

L'invention ne concerne pas les catalyseurs susceptibles d'intervenir dans sa mise en oeuvre. L'on peut, en effet, employer tout catalyseur connu présentant une activité pour l'isomérisation des paraffines linéaires en paraffines ramifiées. Dans ce domaine, de nombreux catalyseurs sont connus de l'homme du métier. Ils comportent généralement une ou plusieurs fonctions de type acide, ainsi qu'une fonction hydrogénante (métal de transition hydrogénant). On citera, à titre d'exemple non limitatif, les catalyseurs à base de chlorure d'aluminium (ou ayant d'autres sites halogénés) et comprenant un ou plusieurs métaux du groupe VIII de la Classification Périodique des Eléments.The invention does not relate to catalysts capable of to intervene in its implementation. We can, in fact, employ any known catalyst exhibiting activity for isomerization of linear paraffins into paraffins branched. In this area, many catalysts are known to those skilled in the art. They usually have a or more acidic functions, as well as a function hydrogenating (hydrogenating transition metal). We will quote, at By way of nonlimiting example, catalysts based on aluminum chloride (or having other halogenated sites) and comprising one or more metals from group VIII of the Periodic Classification of the Elements.

D'autres caractéristiques et avantages de l'invention apparaítront à la lecture de la description qui va suivre de différents modes de mise en oeuvre de celle-ci. Dans cette description, on se réfèrera aux dessins annexés, dans lesquels:

  • la figure 1 est une vue schématique d'une unité d'isomérisation incluant une injection d'un fluide d'appoint, conformément à l'invention; .
  • les figures 2, 3, 4, 5 sont des variantes de réalisation de la figure 1;
  • la figure 6 est une vue synoptique illustrant les relations d'une unité d'isomérisation avec d'autres unités pétrolières, telles qu'elles existent dans l'art antérieur, d'une part, et telles que modifiées conformément à l'invention, d'autre part.
Other characteristics and advantages of the invention will appear on reading the description which follows of different modes of implementation thereof. In this description, reference will be made to the appended drawings, in which:
  • Figure 1 is a schematic view of an isomerization unit including an injection of a makeup fluid, according to the invention; .
  • Figures 2, 3, 4, 5 are alternative embodiments of Figure 1;
  • FIG. 6 is a block diagram illustrating the relationships of an isomerization unit with other petroleum units, as they exist in the prior art, on the one hand, and as modified in accordance with the invention, on the other hand.

La figure 1 représente une unité pour l'isomérisation de coupes contenant des paraffines linéaires à 5 ou 6 atomes de carbone. Cette charge arrive par la ligne 1, dans laquelle de l'hydrogène et éventuellement des gaz de recycle sont introduits par la ligne 2. Le mélange réactionnel ainsi obtenu est acheminé par la ligne 33 vers deux échangeurs de chaleur 3 et 4, à contre-courant des effluents des deux réacteurs d'isomérisation de l'unité. Le mélange réactionnel ainsi réchauffé est ensuite introduit dans un premier réacteur 5, ou réacteur amont. Ce dernier renferme un catalyseur d'isomérisation réparti dans un lit catalytique 6, qui occupe une majeure partie de la hauteur du réacteur 5. L'effluent de ce dernier, après être passé dans l'échangeur 4, est ensuite introduit par la ligne 7 dans le second réacteur 8, ou réacteur aval, qui est lui aussi chargé avec un catalyseur d'isomérisation réparti dans un lit catalytique 9.FIG. 1 represents a unit for the isomerization of sections containing linear paraffins with 5 or 6 atoms of carbon. This charge arrives via line 1, in which hydrogen and possibly recycle gases are introduced by line 2. The reaction mixture thus obtained is routed by line 33 to two heat exchangers heat 3 and 4, against the effluent from both unit isomerization reactors. The reaction mixture thus reheated is then introduced into a first reactor 5, or upstream reactor. The latter contains a isomerization catalyst distributed in a catalytic bed 6, which occupies most of the height of the reactor 5. The effluent from the latter, after passing through the exchanger 4, is then introduced via line 7 into the second reactor 8, or downstream reactor, which is also loaded with an isomerization catalyst distributed in a catalytic bed 9.

Dans le cas présent, la charge à traiter circule de haut en bas dans les réacteurs 5 et 8, mais elle pourrait naturellement y circuler de bas en haut.In the present case, the load to be treated flows from high down in reactors 5 and 8, but it could naturally circulate there from bottom to top.

L'effluent du réacteur aval 8, qui contient une charge enrichie en isoparaffines, est évacué par la ligne 10 et, après avoir traversé l'échangeur 3, est dirigé vers un ensemble de séparation des produits (non représenté). Le dispositif comprend en outre des systèmes de vannes, non représentés, permettant d'interrompre indépendamment l'alimentation des réacteurs 5 et 8 et/ou d'inverser le sens de circulation du mélange réactionnel.The effluent from the downstream reactor 8, which contains a feed enriched in isoparaffins, is evacuated via line 10 and, after crossing the interchange 3, is directed towards a product separation assembly (not shown). The device further includes valve systems, not represented, allowing to interrupt independently feeding reactors 5 and 8 and / or reversing the direction circulation of the reaction mixture.

Conformément à l'invention, un fluide d'appoint est injecté dans le réacteur amont 5, par l'intermédiaire d'une canne 11 sensiblement perpendiculaire à l'axe du réacteur et qui débouche directement dans le lit catalytique, dans la première moitié de celui-ci. Cette canne est pourvue de fentes latérales, non représentées, permettant une meilleure distribution.According to the invention, a make-up fluid is injected into the upstream reactor 5, via a rod 11 substantially perpendicular to the axis of the reactor and which leads directly into the catalytic bed, into the first half of it. This rod is provided with side slits, not shown, allowing better distribution.

Selon une variante de réalisation représentée à la figure 2, le lit catalytique 6 du réacteur amont 5 peut être séparé en une section amont 12 et une section aval 13, qui renferment le même catalyseur d'isomérisation. La canne 11a d'introduction de fluide d'appoint pénètre alors au sein du réacteur entre les deux sections catalytiques 12 et 13.According to an alternative embodiment shown in FIG. 2, the catalytic bed 6 of the upstream reactor 5 can be separated into an upstream section 12 and a downstream section 13, which contain the same isomerization catalyst. The rod 11 a for introducing make-up fluid then enters the reactor between the two catalytic sections 12 and 13.

Selon une autre variante de réalisation représentée à la figure 3, un système d'injection étagé 11b permet l'introduction de fluide d'appoint à plusieurs niveaux dans la première moitié du lit catalytique 6 du réacteur 5.According to another alternative embodiment shown in FIG. 3, a stepped injection system 11b allows the introduction of make-up fluid at several levels in the first half of the catalytic bed 6 of the reactor 5.

Selon une autre variante de réalisation représentée à la figure 4, un système d'injection 11c de fluide d'appoint débouche dans le réacteur 5 de manière sensiblement parallèle à l'axe de ce dernier, au niveau de l'orifice permettant l'introduction du mélange réactionnel (charge et hydrogène) acheminé au réacteur par la ligne 33.According to another alternative embodiment shown in FIG. 4, an injection system 11 c of make-up fluid opens into the reactor 5 in a manner substantially parallel to the axis of the latter, at the orifice allowing the introduction of the reaction mixture (feed and hydrogen) supplied to the reactor via line 33.

Selon encore une autre variante de réalisation représentée à la figure 5, une ligne 11d d'alimentation en fluide d'appoint débouche dans la ligne d'arrivée 33 du mélange réactionnel (charge et hydrogène), immédiatement en amont du premier réacteur d'isomérisation 5. According to yet another alternative embodiment represented in FIG. 5, a line 11 d for supplying make-up fluid opens into the inlet line 33 of the reaction mixture (feed and hydrogen), immediately upstream of the first reactor. isomerization 5.

Il est à noter que, dans le cas où l'unité d'isomérisation comporte au moins deux réacteurs en série, l'injection de fluide d'appoint a toujours lieu au niveau du réacteur amont, dans la mesure où l'hydrogénation du benzène est beaucoup plus rapide que l'isomérisation des paraffines elle-même et se déroule uniquement au sein du réacteur amont.It should be noted that, in case the unit isomerization comprises at least two reactors in series, make-up fluid injection always takes place at the upstream reactor, insofar as the hydrogenation of benzene is much faster than isomerization of paraffins itself and takes place only within the reactor upstream.

Par ailleurs, dans ces unités comportant deux réacteurs ou plus, il est usuel d'inverser le sens de circulation du mélange réactionnel, notamment à la suite du remplacement du lit catalytique de l'un des réacteurs.. Le réacteur amont devient alors réacteur aval et inversement. Il faut alors déplacer en conséquence le(s) point(s) d'introduction du fluide d'appoint, de manière à ce que cette introduction ait toujours lieu au niveau du réacteur amont.Furthermore, in these units comprising two reactors or more, it is usual to reverse the direction of circulation of the reaction mixture, in particular following the replacement of the catalytic bed of one of the reactors. The upstream reactor then becomes downstream reactor and vice versa. We must then move the entry point (s) accordingly make-up fluid, so that this introduction has always take place at the level of the upstream reactor.

C'est pourquoi il peut être judicieux de prévoir un système d'injection de fluide d'appoint sur chacun des deux réacteurs placés à l'extrémité de la série. Bien entendu, un seul de ces systèmes fonctionnera à la fois, selon le sens de circulation du mélange réactionnel.This is why it may be wise to plan a make-up fluid injection system on each of the two reactors placed at the end of the series. Of course, a only one of these systems will work at a time, depending on the meaning circulation of the reaction mixture.

Enfin, dans le cas d'une unité ne comprenant qu'un seul réacteur, l'injection du fluide d'appoint est similaire à celle représentée aux figures 1 à 5.Finally, in the case of a unit comprising only one injection fluid injection is similar to that shown in Figures 1 to 5.

La figure 6 montre comment l'invention peut permettre d'améliorer les relations existant entre l'unité d'isomérisation et d'autres unités pétrolières.FIG. 6 shows how the invention can allow improve the relationships between the unit isomerization and other petroleum units.

Comme il est représenté sur cette figure, l'essence de distillation directe (ou "straight-run"), qui correspond à une coupe distillant entre environ 20 et 180°C, sort par la ligne 14 d'une unité de fractionnement principale, non représentée.As shown in this figure, the essence of direct distillation (or "straight-run"), which corresponds to a distilling cut between about 20 and 180 ° C, comes out through the line 14 of a main fractionation unit, not represented.

Cette essence de distillation directe est alors divisée, au sein du séparateur 15, en une essence légère, évacuée par la ligne 16, et une essence lourde, évacuée par la ligne 17, le point de coupe entre ces deux fractions se situant de manière usuelle entre 70 et 90°C. Puis l'essence légère est débarrassée, dans le déisopentaniseur 18, de son isopentane, et se trouve dirigée par la ligne 1 vers l'unité d'isomérisation.This direct distillation essence is then divided, within the separator 15, in a light essence, discharged by line 16, and a heavy fuel, discharged through line 17, the cutting point between these two fractions being from usual way between 70 and 90 ° C. Then light petrol is freed, in the deisopentanizer 18, of its isopentane, and is directed by line 1 to the unit isomerization.

La fraction riche en isopentane, qui est un composé à haut indice d'octane ne nécessitant donc pas de traitement d'isomération, est évacuée par la ligne 19. L'essence légère appauvrie en isopentane traverse alors les deux réacteurs d'isomérisation 5 et 8 tels que décrits précédemment, et la charge enrichie en isoparaffines en est extraite par la ligne 10.The fraction rich in isopentane, which is a compound with high octane number therefore requiring no treatment isomerization, is evacuated via line 19. Light petrol depleted in isopentane then crosses the two reactors isomerization 5 and 8 as described above, and the load enriched in isoparaffins is extracted therefrom by line 10.

Cette charge est ensuite séparée, au sein du stabilisateur 20, en une coupe de tête 21, constituée de composés à quatre atomes de carbone au maximum, et une coupe de fond 22 de composés plus lourds.: Cette dernière est ensuite dirigée vers le déisohexaniseur 23, où elle se trouve divisée en un isomérat 26, constitué d'isoparaffines à 5 ou 6 atomes de carbone, et une coupe lourde 25, constituée essentiellement de naphtènes et de paraffines à 7 atomes de carbone ou plus.This charge is then separated, within the stabilizer 20, in a head section 21, consisting of compounds with up to four carbon atoms, and a cut background 22 of heavier compounds .: The latter is then directed to the deisohexanizer 23, where it found divided into an isomerate 26, consisting of isoparaffins with 5 or 6 carbon atoms, and a heavy cut 25, essentially consisting of naphthenes and paraffins at 7 carbon atoms or more.

En outre, une coupe riche en naphtènes et en paraffines non isomérisées à 5 ou 6 atomes de carbone, est traditionnellement recyclée en amont du premier réacteur par l'intermédiaire de la ligne 24. Ainsi, cette coupe, qui ne contient pas de benzène, effectue non seulement un passage supplémentaire dans l'unité d'isomérisation, mais permet aussi de diluer la charge fraíche admise dans l'unité, de manière à abaisser la teneur en benzène de la charge combinée ainsi obtenue.In addition, a cut rich in naphthenes and paraffins not isomerized to 5 or 6 carbon atoms, is traditionally recycled upstream of the first reactor by through line 24. So this cut, which doesn't contains no benzene, not only passes additional in the isomerization unit, but allows also to dilute the fresh charge allowed in the unit, to so as to lower the benzene content of the charge combined thus obtained.

En faisant toujours référence à la figure 6, l'essence lourde évacuée du séparateur 15 par la ligne 17 est dirigée vers l'unité de reformage 27, au sein de laquelle elle subit entre autres des réactions d'aromatisation, qui contribuent à augmenter sa teneur en produits aromatiques, dont du benzène. Le réformat ainsi produit est ensuite séparé au niveau du fractionnement 28 en un réformat lourd 29, dont le point d'ébullition est supérieur à environ 90°C, qui est acheminé vers le pool essences, et un réformat léger 31, dont le point d'ébullition est compris entre environ 30°C et 90°C.Still referring to Figure 6, the essence heavy discharged from separator 15 via line 17 is directed towards the reforming unit 27, within which it undergoes among others aromatization reactions, which contribute to increase its content of aromatic products, including benzene. The reformate thus produced is then separated at level of fractionation 28 into a heavy reformate 29, the boiling point is above about 90 ° C, which is routed to the gasoline pool, and a light reformate 31, whose boiling point is between about 30 ° C and 90 ° C.

L'essentiel du benzène produit dans le reformage est présent dans le réformat léger 31. Afin de réduire la teneur en benzène de la coupe essence finale, il est donc judicieux d'envoyer le réformat léger 31 vers les réacteurs 5, 8, de l'unité d'isomérisation. Cependant, cette dernière ne peut traiter des charges à teneur très élevée en benzène, de sorte qu'il est nécessaire soit de soutirer du fractionnement par la ligne 32 une coupe benzène qui est difficilement valorisable, car trop impure, soit d'augmenter le débit de recycle de la ligne 24, afin d'abaisser la teneur en benzène de la charge combinée entrant dans le réacteur 5, au détriment de la qualité des réactions d'isomérisation proprement dites.Most of the benzene produced in reforming is present in light reformate 31. In order to reduce the content in benzene from the final gasoline cut, so it makes sense send the light reformate 31 to reactors 5, 8, the isomerization unit. However, the latter cannot treat loads with a very high benzene content, so it is necessary either to draw from fractionation by line 32 a benzene cut which is difficult to value, because too impure, or to increase the recycling rate of line 24, in order to lower the benzene content of the combined charge entering the reactor 5, to the detriment of the quality of the reactions isomerization proper.

La suite de la description va mettre en exergue les modifications que l'invention permet d'apporter, en particulier en ce qui concerne l'utilisation du réformat léger 31 et de la fraction 24 recyclée à l'isomérisation.The rest of the description will highlight the modifications that the invention makes possible, in especially regarding the use of the reformate light 31 and fraction 24 recycled to isomerization.

Conformément à l'invention, un moyen 11 d'injection d'un fluide d'appoint, pénètre dans le lit catalytique du réacteur amont 5. Le fluide d'appoint est constitué de composés comprenant au plus 4 atomes de carbone issus par la ligne 35 de la coupe de tête, évacuée en 21, du stabilisateur 20. De la sorte, l'unité d'isomérisation est susceptible de traiter le cas échéant des charges à teneur en benzène plus élevée que dans l'art antérieur. Ainsi, le doublement de la quantité de benzène présent dans la charge peut être compensé thermiquement par un appoint de fluide léger (densité inférieure ou égale à celle du normal-pentane), dont le débit sera ajusté en fonction de la teneur en benzène de la charge à isomériser.According to the invention, a means 11 for injecting a make-up fluid, enters the catalytic bed of the upstream reactor 5. The make-up fluid consists of compounds comprising at most 4 carbon atoms derived from the line 35 of the head cup, discharged at 21, from stabilizer 20. In this way, the isomerization unit is likely to deal with charges with content higher in benzene than in the prior art. So the Doubling the amount of benzene present in the charge can be thermally compensated by adding fluid light (density less than or equal to that of normal-pentane), the flow rate of which will be adjusted according to the benzene content of the feed to be isomerized.

Cette augmentation de la teneur en benzène admissible permet une plus grande flexibilité au niveau de l'isomérisation et des unités environnantes. Ainsi, il est possible d'envoyer en charge de l'isomérisation un débit plus élevé de réformat léger 31, sans augmenter le débit du recycle 24, qui nuit à la qualité des réactions d'isomérisation. Le soutirage de la coupe benzène 32 mal valorisable sera quant à lui moins conséquent.This increase in the allowable benzene content allows greater flexibility in isomerization and surrounding units. So it is possible to send a charge for isomerization higher of light reformate 31, without increasing the flow of the recycles 24, which affects the quality of the reactions isomerization. Filling the benzene 32 cut poorly recoverable will be less significant.

Il devient également possible de remplacer le recycle 24 par un recycle 34, immédiatement en aval du premier réacteur 5 d'isomérisation. Il en résulte une bien meilleure valorisation de ce premier réacteur 5, et une amélioration sensible des réactions d'isomérisation qui s'y produisent : d'une part, le débit de charge y est plus faible ; d'autre part, on évite ainsi de faire circuler dans le premier réacteur un recycle 24, et donc les composés naphténiques présents dans ce recycle, qui inhibent les réactions d'isomérisation.It also becomes possible to replace the recycle 24 by a recycle 34, immediately downstream of the first reactor 5 isomerization. This results in a much better upgrading of this first reactor 5, and an improvement sensitive to the isomerization reactions which occur there: on the one hand, the charge flow rate is lower there; else share, thus avoiding circulating in the first reactor a recycles 24, and therefore naphthenic compounds present in this recycle, which inhibits reactions isomerization.

Les exemples ci-après, qui n'ont pas de caractère limitatif, sont destinés à illustrer la mise en oeuvre de l'invention et les avantages de celle-ci.The following examples, which have no character are intended to illustrate the implementation of the invention and the advantages thereof.

Exemple 1Example 1

Cet exemple a pour but d'illustrer les limites des procédés d'isomérisation d'essences classiques, dans le cas du traitement de charges à teneur élevée en benzène.The purpose of this example is to illustrate the limits of conventional gasoline isomerization processes, in the case treatment of loads with high benzene content.

Une coupe pétrolière de type essence légère de distillation directe (charge n°1) possède les propriétés suivantes:

  • point 5% (en volume) de distillation A.S.T.M.: 31°C,
  • point 95% (en volume) de distillation A.S.T.M : 86°C,
  • teneur en soufre: 1 ppm en poids,
  • teneur en azote: 1 ppm en poids,
  • teneur en benzène: 3,5% en poids,
  • densité à 15°C: 0,680.
A light petrol type petroleum cut of direct distillation (charge n ° 1) has the following properties:
  • 5% point (by volume) of ASTM distillation: 31 ° C.,
  • 95% point (by volume) of ASTM distillation: 86 ° C.,
  • sulfur content: 1 ppm by weight,
  • nitrogen content: 1 ppm by weight,
  • benzene content: 3.5% by weight,
  • density at 15 ° C: 0.680.

Cette charge, dont le débit est de 91,7 t/h, est combinée avec un mélange gazeux riche en hydrogène (20% en poids d'hydrogène), introduit à un débit de 2 t/h. Ce mélange réactionnel est alors réchauffé jusqu'à 133°C, puis traité dans une unité d'isomérisation d'essences classique comportant deux réacteurs en série, fonctionnant à une pression de 31.105 Pa. La température relevée en sortie du premier réacteur est de 180°C.This charge, the flow rate of which is 91.7 t / h, is combined with a gaseous mixture rich in hydrogen (20% by weight of hydrogen), introduced at a flow rate of 2 t / h. This reaction mixture is then warmed up to 133 ° C., then treated in a conventional gasoline isomerization unit comprising two reactors in series, operating at a pressure of 31 × 10 5 Pa. The temperature recorded at the outlet of the first reactor is 180 ° C.

On refait le test, avec une charge conforme à celle décrite ci-avant, mais à laquelle on incorpore une forte teneur en benzène: cette charge n°2 possède une teneur en benzène de 7,66 % en poids et une densité à 15°C de 0,687. Les autres propriétés demeurent globalement inchangées par rapport à la charge n°1.We repeat the test, with a charge in accordance with that described above, but which incorporates a strong benzene content: this charge No. 2 has a content of benzene of 7.66% by weight and a density at 15 ° C of 0.687. The other properties remain globally unchanged by in relation to charge # 1.

Cette charge n°2 est traitée dans les mêmes conditions opératoires que celles mentionnées ci-avant pour le traitement de la charge n°1, à l'exception du débit de gaz riche en hydrogène, qui est porté à 3,5 t/h (de manière connue en soi, l'isomérisation de charges riches en benzène nécessite une quantité accrue d'hydrogène dans le milieu réactionnel, compte tenu de la consommation supplémentaire d'hydrogène induite par l'hydrogénation du benzène).This charge n ° 2 is treated under the same conditions than those mentioned above for the treatment of charge # 1, except gas flow rich in hydrogen, which is brought to 3.5 t / h (so known per se, the isomerization of charges rich in benzene requires an increased amount of hydrogen in the medium reactive, taking into account the additional consumption hydrogen induced by the hydrogenation of benzene).

La température relevée en sortie du premier réacteur est alors de 193°C. Il y a donc eu une augmentation de température de 13°C dans ce réacteur, due à la forte quantité de chaleur dégagée par l'hydrogénation du supplément de benzène présent dans la charge n°2. A terme, cette augmentation de température dans le premier réacteur risque non seulement d'endommager le catalyseur et l'unité, mais également de diminuer les rendements de la réaction d'isomérisation (meilleurs à basse température).The temperature recorded at the outlet of the first reactor is then 193 ° C. So there was an increase in temperature of 13 ° C in this reactor, due to the high quantity of heat given off by the hydrogenation of the supplement benzene present in charge # 2. Ultimately, this temperature increase in the first reactor risk not only damage the catalyst and the unit, but also to decrease the reaction yields isomerization (better at low temperature).

Cet exemple montre donc combien les procédés de l'art antérieur s'avèrent peu adaptés à l'isomérisation de charges à forte teneur en benzène.This example therefore shows how the processes of art previous prove to be poorly suited to isomerization of charges high in benzene.

Exemple 2Example 2

Dans cet exemple, la charge riche en benzène décrite ci-avant (charge n°2) est traitée cette fois-ci selon le procédé d'isomérisation conforme à l'invention. Un fluide d'appoint est donc introduit dans le lit catalytique du premier réacteur, au niveau du premier tiers du lit catalytique (aux 2/7 de ce lit, exactement), et avec un débit de 30Nm3 par m3 de charge. Deux températures d'introduction du fluide d'appoint ont été testées: 30°C (température inférieure à celle du milieu réactionnel) et 145°C (température de l'ordre de celle du milieu réactionnel).In this example, the charge rich in benzene described above (charge n ° 2) is treated this time according to the isomerization process according to the invention. A fluid make-up is therefore introduced into the catalytic bed of the first reactor, at the level of the first third of the bed catalytic (exactly 2/7 of this bed), and with a flow of 30Nm3 per m3 of load. Two introduction temperatures make-up fluid have been tested: 30 ° C (temperature lower than that of the reaction medium) and 145 ° C. (temperature of the order of that of the reaction medium).

Différentes compositions de fluide d'appoint, mentionnées dans le Tableau I ci-après, ont été testées successivement. Fluide Composition (en % en poids) Densité (40°C, 1,0134 Pa) F1 2 % H2 + 12 % CH4 + 18 % C2H6 + 25 % C3H8 + 43 % C4H10 1,04.10-3 F2 2 % H2 + 80 % CH4 + 16 % C2H6 +2 % C3H3 0,59.10-3 F4 100 % CH4 0,62.10-3 F5 100 % C2H6 1,16.10-3 F6 100 % C3H8 1,72.10-3 F7 100 % nC4H10 2,28.10-3 Different makeup fluid compositions, mentioned in Table I below, were tested successively. Fluid Composition (in% by weight) Density (40 ° C, 1.0134 Pa) F1 2% H 2 + 12% CH 4 + 18% C 2 H 6 + 25% C 3 H 8 + 43% C 4 H 10 1.04.10 -3 F2 2% H 2 + 80% CH 4 + 16% C 2 H 6 + 2% C 3 H 3 0.59.10 -3 F4 100% CH 4 0.62.10 -3 F5 100% C 2 H 6 1.16.10 -3 F6 100% C 3 H 8 1.72.10 -3 F7 100% nC 4 H 10 2.28.10 -3

Le fluide F1 correspond à un mélange gazeux dU type de ceux que peut récupérer en tête d'une colonne de fractionnement située en aval de l'unité d'isomérisation (colonne dite de stabilisation).The fluid F1 corresponds to a gaseous mixture of the type of those that can recover at the head of a column of fractionation located downstream of the isomerization unit (so-called stabilization column).

A 40°C, sous une pression de 1,0134.105 Pa (1 atmosphère), tous les fluides considérés se trouvent à l'été gazeux et ont une densité inférieure à celle du pentane considéré dans les mêmes conditions.At 40 ° C, under a pressure of 1.0134.10 5 Pa (1 atmosphere), all the fluids considered are in the gaseous summer and have a density lower than that of the pentane considered under the same conditions.

Pour le test d'isomérisation, les conditions opératoires sont identiques à celles décrites dans l'Exemple 1 pour le traitement de la charge n°2, et la température d'entrée du mélange réactionnel dans le premier réacteur d'isomérisation est notamment maintenue à 133°C.For the isomerization test, the operating conditions are identical to those described in Example 1 for the treatment of the charge n ° 2, and the inlet temperature of the reaction mixture in the first isomerization reactor is notably maintained at 133 ° C.

Le Tableau II ci-après rassemble les résultats obtenus en terme de température de sortie du premier réacteur. Fluide d'appoint Température de sortie du premier réacteur F1 180 °C 183 °C F2 180 °C 181 °C F4 179 °C 180 °C F5 180 °C 182°C F6 179 °C 184 °C F7 181 °C 187 °C Des résultats identiques à ceux exposés ci-avant ont été obtenus en introduisant le fluide d'appoint immédiatement en amont du premier réacteur d'isomérisation, entre le dispositif de réchauffement du mélange réactionnel le plus en aval et le point d'injection dudit mélange dans le premier réacteur.Table II below collates the results obtained in terms of outlet temperature from the first reactor. Make-up fluid First reactor outlet temperature F1 180 ° C 183 ° C F2 180 ° C 181 ° C F4 179 ° C 180 ° C F5 180 ° C 182 ° C F6 179 ° C 184 ° C F7 181 ° C 187 ° C Results identical to those set out above were obtained by introducing the make-up fluid immediately upstream of the first isomerization reactor, between the device for heating the reaction mixture most downstream and the point of injection of said mixture into the first reactor.

Comme le montre le Tableau II ci-dessus, l'introduction d'un fluide d'appoint léger permet de compenser l'excès de chaleur qui se dégage dans le premier réacteur en présence d'une charge riche en benzène. On parvient ainsi à abaisser la température régnant dans ce réacteur et, notamment, à ramener sa température de sortie à une valeur identique à, ou proche de, la température observée en isomérisation de charges à teneur limitée en benzène (charge n°1).As shown in Table II above, the introduction a light make-up fluid compensates for the excess of heat given off in the first reactor present a charge rich in benzene. We thus manage to lower the temperature prevailing in this reactor and, in particular, at reduce its outlet temperature to a value identical to, or close to, the temperature observed in isomerization of charges with limited benzene content (charge # 1).

Par ailleurs, des résultats différents sont obtenus selon le fluide d'appoint utilisé. En particulier, lorsque le fluide d'appoint est introduit à une température élevée, l'abaissement de la température du premier réacteur est plus important avec des fluides légers. Il est donc possible d'adapter la composition du fluide introduit à la teneur en benzène de la charge à isomériser, avec pour conséquence, une excellente flexibilité du procédé selon l'invention.Furthermore, different results are obtained depending on the make-up fluid used. In particular, when the make-up fluid is introduced at a high temperature, lowering the temperature of the first reactor is more important with light fluids. It is therefore possible to adapt the composition of the fluid introduced to the content of benzene of the charge to be isomerized, with the consequence excellent flexibility of the process according to the invention.

Exemple 3Example 3

Dans cet exemple, dans les essais 2 à 4, la charge riche en benzène (charge n°2 de l'Exemple 1) est isomérisée, en appliquant le procédé conforme à l'invention et dans des conditions opératoires identiques à celles de l'Exemple n°2, mais en faisant varier le débit du fluide d'appoint. Les trois essais mentionnés dans le Tableau III ci-dessous ont été effectués avec le même fluide F2, introduit dans le lit catalytique du premier réacteur à une température de 145°C.In this example, in tests 2 to 4, the rich charge into benzene (charge No. 2 of Example 1) is isomerized, applying the process according to the invention and in operating conditions identical to those of Example 2, but by varying the flow rate of the make-up fluid. The three tests mentioned in Table III below have were carried out with the same F2 fluid, introduced into the bed catalytic of the first reactor at a temperature of 145 ° C.

L'essai 1 correspond à un débit de fluide d'appoint nul (art antérieur). Essai Débit du fluide
d'appoint
(Nm3 par m3 de
charge) Température de
sortie du premier
réacteur (°C) 1 0 193 2 10 188 3 30 181 4 60 173 Test 1 corresponds to a zero makeup fluid flow rate (prior art). Trial Fluid flow
extra
(Nm 3 per m 3 of
charge) Temperature
release of the first
reactor (° C) 1 0 193 2 10 188 3 30 181 4 60 173

Cet exemple illustre l'excellent contrôle thermique auquel permet d'accéder l'invention. Ce contrôle est extrêmement précis et flexible, puisque le débit du fluide d'appoint peut être optimisé en fonction des caractéristiques de la charge à traiter et, notamment, de sa teneur en benzène.This example illustrates the excellent thermal control to which the invention gives access. This control is extremely precise and flexible, since the fluid flow can be optimized according to the characteristics the load to be treated and, in particular, its content benzene.

Exemple 4Example 4

Cet exemple permet de préciser les conditions dans lesquelles le procédé conforme à l'invention doit être mis en oeuvre, et notamment la nature des fluides d'appoint susceptibles d'être employés.This example specifies the conditions in which the process according to the invention must be implemented work, and in particular the nature of the make-up fluids likely to be employed.

Les conditions opératoires sont identiques à celles de l'Exemple 2.The operating conditions are identical to those of Example 2.

Différents fluides d'appoint ont été testés successivement :

  • F1 et F5 sont les fluides déjà mentionnés dans l'Exemple 2 et correspondent aux conditions de l'invention : fluides gazeux à 40°C, sous une pression de 1,0134.105 Pa (1 atmosphère) et de densité inférieure à celle du pentane considéré dans les mêmes conditions.
  • F9 et F10 sont des fluides plus lourds que le pentane.
Different make-up fluids have been tested successively:
  • F1 and F5 are the fluids already mentioned in Example 2 and correspond to the conditions of the invention: gaseous fluids at 40 ° C, under a pressure of 1.0134.10 5 Pa (1 atmosphere) and of density lower than that of pentane considered under the same conditions.
  • F9 and F10 are heavier fluids than pentane.

Ces fluides sont tous injectés dans le lit catalytique du premier réacteur à une température de 145°C, et un débit de 30Nm3 par m3 de charge.These fluids are all injected into the catalytic bed of the first reactor at a temperature of 145 ° C., and a flow rate of 30Nm 3 per m 3 of charge.

Le Tableau IV ci-après expose les natures des fluides testés ainsi que les résultats obtenus lors des essais d'isomérisation de la charge N°2 riche en benzène. Fluide Composition Etat physique
(densité) à
40°C,
1,0134.105Pa Température
sortie
1er réacteur (°C) F1 Mélange (H2, C1 à C4) gazeux (1,04.10-3) 183 F5 100% C2H3 gazeux (1,16.10-3) 182 F9 100% nC6H14 liquide 192 F10 100% nC9H20 liquide 196 Table IV below shows the nature of the fluids tested as well as the results obtained during the isomerization tests of charge No. 2 rich in benzene. Fluid Composition Physical state
(density) to
40 ° C,
1.0134.10 5 Pa Temperature
exit
1 st reactor (° C) F1 Mixture (H 2 , C 1 to C 4 ) gaseous (1.04.10 -3 ) 183 F5 100% C 2 H 3 gaseous (1,16.10 -3 ) 182 F9 100% nC 6 H 14 liquid 192 F10 100% nC 9 H 20 liquid 196

Ces résultats soulignent la validité des critères retenus pour sélectionner les fluides d'appoint susceptibles d'être employés dans l'invention.These results underline the validity of the criteria selected to select the likely make-up fluids to be employed in the invention.

Pour des fluides trop lourds, et en particulier plus lourds que le pentane, l'effet thermodynamique décrit ne se produit plus et l'injection de fluide d'appoint ne permet plus d'abaisser la température du premier réacteur. On constate même que, lorsqu'un tel fluide est introduit à une température supérieure ou égale à la température d'entrée dans le réacteur, comme c'est le cas dans le présent exemple, l'on risque d'aboutir à une élévation supplémentaire de la température de ce réacteur (voir cas du fluide F10).For excessively heavy fluids, and in particular more heavier than pentane, the thermodynamic effect described is not produces more and the injection of make-up fluid does not allow more to lower the temperature of the first reactor. We even notes that when such a fluid is introduced to a temperature greater than or equal to the inlet temperature in the reactor, as is the case in this example, there is a risk of further raising the temperature of this reactor (see case of fluid F10).

Claims (16)

  1. A process for isomerisation of a hydrocarbon feedstock containing a substantial quantity of paraffinic hydrocarbons with 5 or 6 carbon atoms and benzene in an amount greater than or equal to 2% by weight, in which the feedstock to be treated passes, in the presence of hydrogen, at a total pressure greater than or equal to 10.105 Pa (10 bar) and an average temperature of between 100 and 200°C, into at least one reactor (5) containing a paraffinic hydrocarbon isomerisation catalyst, said process being characterised in that a make-up fluid is introduced into the upstream part of the reaction zone, which fluid, at 40°C and atmospheric pressure (1, 0134.105 Pa), is in the gaseous state and has a density lower than or equal to that of normal-pentane under the same conditions, this make-up fluid containing at least 98% by weight of hydrocarbons comprising from one to four carbon atoms.
  2. A process according to claim 1, characterised in that the hydrocarbons comprising from one to four carbon atoms come from a column (20) for fractionating isomerisation unit effluents.
  3. A process according to either one of claims 1 and 2, characterised in that said make-up fluid also comprises hydrocarbons with six or seven carbon atoms, and/or inert gases such as nitrogen, or any other suitable light fluid.
  4. A process according to one of claims 1 to 3, characterised in that make-up fluid is injected into the upstream part of the first isomerisation reactor (5), i.e. into the zone extending from the level at which the reaction mixture (feedstock and hydrogen) is introduced into this reactor as far as halfway down the catalytic bed (6).
  5. A process according to any one of the preceding claims, characterised in that make-up fluid is injected immediately upstream of the first reactor, that is to say after full preheating of the reaction mixture (feedstock and hydrogen) and prior to injection of said mixture into the first reactor (5).
  6. A process according to any one of the preceding claims, characterised in that said make-up fluid is injected at a flow rate of 5 to 150 Nm3 per m3 of feedstock.
  7. A process according to claim 6, characterised in that said make-up fluid is injected at a flow rate of 5 to 60 Nm3 per m3 of feedstock.
  8. A process according to any one of the preceding claims, characterised in that said make-up fluid is injected at a temperature lover than or equal to that of the reaction medium and, preferably, of between 20 and 180°C.
  9. A process according to any one of the preceding claims, in which the isomerisation unit comprises a plurality of reactors in series (5, 8), characterised in that a cut rich in non-isomerised paraffins with 5 or 6 carbon atoms and which generally contains naphthenes, originating from the separation and treatment of the effluents from the isomerisation unit, is recycled immediately downstream of the first reactor (5).
  10. A process according to one of claims 1 to 9, characterised in that make-up fluid is introduced into the line supplying the reaction zone with reaction mixture (feedstock and hydrogen), between a means (4) for heating said mixture and the point of injection thereof into the reaction zone (5).
  11. A process according to one of claims 1 to 9, characterised in that make-up fluid is introduced into the reaction zone (5) upstream of a dense catalyst bed (6) and/or within the first half of said bed.
  12. A process according to claim 11, characterised in that, with a view to ensuring better distribution of the make-up fluid, the latter is introduced by means of a pipe or tube provided with lateral slots or a plurality of orifices.
  13. A process according to one of claims 11 and 12, characterised in that, with a view to distributing the make-up fluid homogeneously over the entire section of the reaction zone (5), said fluid is introduced by means of a diffuser.
  14. A process according to one of claims 1 to 13, characterised in that make-up fluid is introduced into the reaction zone transversely relative to the axis of the reactor (5), substantially perpendicularly to the axis of said reactor.
  15. A process according to one of claims 1 to 13, characterised in that the make-up fluid is introduced into the reaction zone via the reaction mixture introduction orifice substantially parallel to the axis of the reactor (5).
  16. A process according to one of claims 1 to 15, in which the reaction zone (5) comprises a bed comprising a distinct upstream section (12) and downstream section (13), characterised in that the make-up fluid is introduced into the reaction zone between the two catalytic sections (12) and (13).
EP99400568A 1998-03-31 1999-03-09 Process for the isomerisation of gasolines with high benzene content Expired - Lifetime EP0949317B1 (en)

Applications Claiming Priority (2)

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FR9803958 1998-03-31
FR9803958A FR2776667B1 (en) 1998-03-31 1998-03-31 METHOD AND DEVICE FOR ISOMERIZING HIGH-BENZENE GASOLINE ESSENCES

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US8590712B2 (en) * 2008-10-08 2013-11-26 Cummins Filtration Ip Inc. Modular filter elements for use in a filter-in-filter cartridge
US8517185B2 (en) * 2008-10-08 2013-08-27 Cummins Filtration Ip, Inc. Two stage fuel water separator and particulate filter utilizing pleated nanofiber filter material
FR2943070B1 (en) 2009-03-12 2012-12-21 Total Raffinage Marketing HYDROCARBON HYDRODEPARAFFIN FLUID FOR THE MANUFACTURE OF INDUSTRIAL, AGRICULTURAL OR DOMESTIC FLUIDS
FR2943064B1 (en) 2009-03-12 2013-12-06 Total Raffinage Marketing HYDROCARBON DILUENT WITH LOW VOC RATES FOR CONSTRUCTION MATERIALS
CN102596862B (en) * 2009-05-15 2015-09-30 康明斯过滤Ip公司 Surface coalescer
US8716544B2 (en) 2011-01-13 2014-05-06 Uop Llc Process for isomerizing a feed stream including one or more C4-C6 hydrocarbons
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US10058808B2 (en) 2012-10-22 2018-08-28 Cummins Filtration Ip, Inc. Composite filter media utilizing bicomponent fibers
FR3015514B1 (en) 2013-12-23 2016-10-28 Total Marketing Services IMPROVED PROCESS FOR DESAROMATIZATION OF PETROLEUM CUTTERS
DE112017002974T5 (en) 2016-07-19 2019-03-07 Cummins Filtration Ip, Inc. KOALESZER WITH PERFORATED LAYER
CN110320307A (en) * 2019-08-02 2019-10-11 中国科学院新疆理化技术研究所 A kind of low temperature sample injection method of controllable punicalagins isomer proportion

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ZA992450B (en) 1999-10-01
ES2221327T3 (en) 2004-12-16
EP0949317A1 (en) 1999-10-13
FR2776667B1 (en) 2000-06-16
US6416657B1 (en) 2002-07-09
DE69917363D1 (en) 2004-06-24
US6881385B2 (en) 2005-04-19
JP4112114B2 (en) 2008-07-02
JPH11323356A (en) 1999-11-26
FR2776667A1 (en) 1999-10-01
US20020139712A1 (en) 2002-10-03
DE69917363T2 (en) 2005-05-12
ATE267239T1 (en) 2004-06-15

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