EP1602705A1 - Process for upgrading a gasoline fraction and transforming in gasoils with additional treatment for increasing the efficiency of the gasoil fraction - Google Patents

Abstract

Process for the adjustment of the relative productions of petrol and gasoil from a petrol cut comprsing 4 - 15 C hydrocarbons to obtain a petrol with an improved octane index and a gasoil fraction with a high cetane index. The process is carried out in the following stages (1) membrane separation, B, of the hydrocarbon charge to obtain a selective separation of most of the linear olefins,cut beta , from the branched chain olefins, cut gamma , comprising petrols of higher octane index than the original charge; (2) (b) oligomerisation, C, of the linear olefins, beta cut, in the effluents from the membrane separation; (c) (3) separation by distillation, D, of the effluents from oligomerisation to give two cuts ; cut delta comprises hydrocarbons of final boiling points lower than 150 - 200[deg]C, and a cut , comprising hydrocarbons of initial boiling points greater than 150 - 200[deg]C; (4) (d) hydrogenation, E, of the cut to obtain a gasoil of cetane index of at least 45; (5) (e) dehydrogenation, F, of the cut delta to convert paraffins to olefins, producing a cut mu which is partly recycled to the membrane separation stage.

Description

Field of the invention

The present invention relates to a method for a simple and economical way to modulate the respective productions of gasoline and diesel. More precisely, according to the process object of the present application, it is possible to transform an initial charge of hydrocarbons in the petrol section, comprising from 4 to 15 carbon atoms and preferably from 4 to 11 carbon atoms, in a gasoline fraction of octane number improved with respect to the load, and a diesel fraction with a high cetane number.

This application is an improvement of the application entitled "Process improvement of gasoline cuts and conversion to diesel "the same inventors and filed on the same day as this application.

The effects of this improvement relate to the efficiency of the diesel fuel obtained, the octane number of the petrol cut obtained, and finally the fact that the essence cut of departure can be of absolutely any composition respecting only the interval number of carbon atoms.

a) les oléfines ramifiées qui possèdent de bons indices d'octane. Cet indice d'octane augmente avec le nombre de ramifications et diminue avec la longueur de chaíne.

b) les oléfines linéaires qui possèdent un faible indice d'octane, cet indice d'octane diminuant fortement avec la longueur de chaíne.

It is known (Fuels and Engines of JC Guibet, Technip Edition, volume I (1987)) that the chemical nature of the olefins contained in the species contributes strongly to the octane number of said gasolines. Olefins can be classified for this reason in two distinct categories:

a) branched olefins which have good octane numbers. This octane number increases with the number of branches and decreases with the chain length.

b) linear olefins which have a low octane number, this octane number decreasing strongly with the length of chain.

The object of the present invention is, from any gasoline cut, to produce an improved octane gasoline cut with respect to the starting gasoline cut, and a diesel fuel cut of cetane number at least equal to 45 and preferably greater than 50.

Moreover, the effluents resulting from the processes of conversion of residues more or less heavy, such as, for example, gasoline cuts from the catalytic cracking process in bed fluidized (FCC) contain an olefin content between 10 and 80%.

These effluents are used in the composition of commercial species for 20 to 40% according to geographical origin (27% in Western Europe and 36% in the USA).

It is likely that in the context of the protection of the environment, commercial species will be oriented in the coming years towards a reduction of the olefin content allowed in the species.

It follows from the foregoing points that the production of low-grade species olefins, but maintaining an acceptable octane number, can only be selecting as the basis for petrol, exclusively or in very large proportions, the branched olefins with a high octane number.

One of the objects of the present invention is to separate from an initial fuel charge the linear olefins of branched olefins.

Another object of the present invention is to provide an alternative allowing a increased flexibility in the management of products from the refinery.

More specifically, the use of the present process can advantageously Modulate the gasoline / diesel proportions obtained at the refinery outlet according to the needs of the market.

Examination of the prior art

There are various processes for the transformation of olefins to increase their octane number.

For example, there may be mentioned aliphatic alkylation between paraffins and olefins to produce high octane gasoline cuts. This process can utilize mineral acids such as sulfuric acid (Symposium on Hydrogen Transfer in Hydrocarbon Processing, 208 ^th National Meeting, American Chemical Society - August 1994, which can be translated as "Symposium on Hydrogen Transfer in processes for hydrocarbon feedstocks "), solvent-soluble catalysts (EP 0714871) or heterogeneous catalysts (US Pat. No. 4,956,518).

By way of example, the isobutane addition processes of alkenes having between 2 and 5 carbon atoms make it possible to produce highly branched molecules having between 7 and 9 carbon atoms, and generally characterized by high octane numbers.

Other transformations using etherification methods are known. branched olefins, such as, for example, those described in patents US 5,633,416 and EP 0451989. These processes make it possible to produce MTBE type ethers (methyl tertio butyl ether), ETBE (ethyl tertiary butyl ether) and TAME (tertiary amyl methyl ether), compounds well known for improving the octane number of gasolines.

In a third way, the oligomerization processes, based essentially on the dimerization and trimerization of light olefins from the catalytic cracking process and possessing between 2 and 4 carbon atoms, allow the production of cuts essences or distillates. An example of such a process is described in patent EP 0734766.

It makes it possible to obtain mainly products having 6 carbon atoms when the olefin used is propylene, and 8 carbon atoms when the olefin is linear butene.

These oligomerization processes are known to give gasoline cuts with good octane numbers, but when done under conditions favoring the formation of heavier cuts, they generate gasoil cuts with a very low index of cetane.

Such examples are furthermore illustrated by US Pat. Nos. 4,456,779 and 4,211,640.

US Pat. No. 5,382,705 proposes to couple the previously described oligomerization and etherification processes in order to produce, from a C ₄ fraction, tertiary alkyl ethers such as MTBE or ETBE and lubricants.

Brief description of the invention:

a) une étape de séparation par membrane de la charge hydrocarbonée (coupe α) dans des conditions permettant la séparation sélective de la majorité des oléfines linéaires présentes dans ladite charge (coupe β), la coupe contenant la majorité des oléfines ramifiées (coupe γ) constituant une essence à fort indice d'octane, c'est à dire supérieur à celui de la charge.

b) une étape de traitement des oléfines linéaires contenues dans les effluents issus de l'étape de séparation sur membrane (coupe β) dans des conditions d'oligomérisation modérées,

c) une étape de séparation par distillation des effluents issus de l'étape d'oligomérisation en au moins deux coupes :

• une coupe légère dite coupe δ, comprenant les hydrocarbures dont le point d'ébullition final est inférieur à une température comprise entre 150°C et 200°C,
• une coupe lourde dite coupe η, comprenant les hydrocarbures dont le point d'ébullition initial est supérieur à une température comprise entre 150°C et 200°C,

d) une étape d' hydrogénation de la coupe η dans des conditions d'obtention d'un gazole à fort indice de cétane, c'est à dire au moins égal à 45, et préférentiellement supérieur à 50.

e) une étape de déshydrogénation (F) de la coupe légère δ, issue de l'étape de séparation par distillation, et produisant une coupe µ qui est au moins en partie recyclée à l'entrée de l'étape de séparation par membrane.

f) facultativement, une étape d'hydrogénation sélective (G) de la coupe µ produisant une coupe λ qui est au moins en partie recyclée à l'entrée de l'étape de séparation par membrane.

The invention relates to a process for converting a hydrocarbon feedstock containing from 4 to 15 carbon atoms and preferably from 4 to 11 carbon atoms, and having any composition of paraffins, olefins and aromatics, said process comprising the following steps :

a) a membrane separation step of the hydrocarbon feedstock (α cut) under conditions allowing the selective separation of the majority of linear olefins present in said feed (β cut), the cut containing the majority of branched olefins (γ cut) constituting a gasoline with high octane number, ie higher than that of the charge.

b) a step of treatment of the linear olefins contained in the effluents resulting from the membrane separation step (β-cut) under moderate oligomerization conditions,

c) a step of separation by distillation of the effluents from the oligomerization step in at least two sections:

• a light section called δ cut, comprising hydrocarbons whose final boiling point is below a temperature of between 150 ° C and 200 ° C,
• a heavy sectional cut, η, comprising hydrocarbons whose initial boiling point is greater than a temperature of between 150 ° C. and 200 ° C.,

d) a step of hydrogenation of the section η under conditions of obtaining a gas oil with a high cetane number, that is to say at least 45, and preferably greater than 50.

e) a step of dehydrogenation (F) of the light cut δ, resulting from the step of separation by distillation, and producing a section μ which is at least partly recycled at the entrance of the membrane separation step.

f) optionally, a step of selective hydrogenation (G) of the section μ producing a cut λ which is at least partly recycled at the entrance of the membrane separation step.

According to a first variant of the process, the δ cut resulting from the separation step by distillation and comprising the majority of linear paraffins and a part of olefins linear, is introduced directly into a catalytic reforming unit supposed to exist on the production site.

According to another variant of the invention, the section μ resulting from the dehydrogenation (F) is recycled at least in part to the entrance of the membrane separation unit (B), the other part of said section μ being sent in mixture with the section γ to form a high octane gasoline.

According to another variant of the invention, the λ cut resulting from the hydrogenation (G) is not completely recycled at the inlet of the membrane separation unit (B), at least one part is mixed with the γ cut to form a high octane gasoline.

In general, in the context of the invention, the oligomerization step is carried out at a pressure of between 0.2 and 10 MPa, with a volume flow rate ratio of catalyst volume (called VVH) between 0.05 and 50 liters / liter / hour, and at a temperature between 15 ° C and 300 ° C.

The oligomerization step is generally carried out in the presence of a catalyst comprising at least one Group VIB metal of the Periodic Table.

The step of separating linear olefins and paraffins from the olefins and branched paraffins on the other hand, is carried out in a so-called separation unit by membrane which will be able to use very diverse types of membrane, the invention being not related to a particular type of membrane.

The membranes that may be used in the context of the invention are preferentially membranes used in nanofiltration and in reverse osmosis (membranes falling under the category of membranes for filtration processes) or membranes used in permeation in gas phase or in pervaporation (re-entrant membrane in the category of membranes for permeation processes).

From the point of view of the materials, these membranes could be either membranes of the type zeolitic, either membranes of polymeric (or organic) type, or even membranes of the ceramic (or mineral) type, that is to say of composite type in the sense that they may consist of a polymer and at least one mineral compound.

The membranes that can be used in the process which is the subject of the invention may also be movie base. For example, in this last category, mention may be made of membranes based on of molecular sieve film, or sieve film-based membranes molecular silicates, aluminosilicates, aluminophosphates, silicoaluminophosphates, metalloaluminophosphates, stanosilicates, or a mixture of at least one of these two types of constituents.

With regard to membranes based on zeolites, mention may be made more particularly membrane based on zeolites of type MFI or ZSM-5, native or having been exchanged with H + ions; Na +; K +; Cs +; Ca +; Ba + and the zeolite membrane type LTA.

In some cases, the method according to the invention may comprise an elimination step at least a part of the nitrogen or basic impurities contained in the initial charge hydrocarbons.

Generally, the initial charge of hydrocarbons will result from a cracking process catalytic, thermal cracking or dehydrogenation of paraffins. It can be introduced in the method that is the subject of the present invention either alone or in admixture with other charges.

Detailed description of the invention

The invention will be better understood on reading FIG. 1 which corresponds to the diagram of FIG. according to the invention and in which the dotted lines optional, the other units in solid lines being obligatory.

According to FIG. 1, the hydrocarbon feedstock is conveyed by line 1 to a unit A of purification.

This unit A makes it possible to eliminate a large part of the nitrogenous and / or basic compounds contained in the load. This elimination, although optional, is necessary when the filler comprises a high level of nitrogen and / or basic compounds, as these constitute a poison for the catalysts of the following steps of the present process.

Said compounds can be removed by adsorption on an acidic solid. This solid can be selected from the group formed by silicoaluminates, titanosilicates, oxides mixed titanium alumina, clays, resins.

The solid may also be chosen from mixed oxides obtained by grafting from less an organometallic compound, organosoluble or water-soluble, of at least one element selected from the group consisting of titanium, zirconium, silicon, germanium, tin, tantalum, niobium, on at least one oxide support such as alumina (forms gamma, delta, eta, alone or in admixture) silica, silica aluminas, titanium silicas, zirconia silicas, Amberlyst type ion exchange resins, or any other solid having any acidity.

A particular embodiment of the invention may consist in implementing a mixture of at least two of the previously described catalysts.

The pressure of the purification unit (A) of the charge is between the pressure atmospheric pressure and 10 MPa, preferably between atmospheric pressure and 5 MPa, and will preferably choose a pressure under which the charge is in the liquid state.

The ratio of the volume flow rate of charge to the volume of catalytic solid (called VVH) is most often between 0.05 liter / liter.hour and 50 liters / liter.hour, preferably between 0.1 liter / liter.hour and 20 liters / liter.hour, and even more preferably, between 0.2 liter / liter / hour and 10 liters / liter / hour.

The temperature of the purification unit (A) is between 15 ° C and 300 ° C, preferably between 15 ° C and 150 ° C, and more preferably between 15 ° C and 60 ° C.

The removal of the nitrogenous and / or basic compounds contained in the feed may also be carried out by washing with an acidic aqueous solution, or by any equivalent means known to those skilled in the art.

The purified α-cut feed is conveyed via line 2 to the separation unit (B). on membrane. In unit (B), the linear olefins and paraffins forming the β-section are separated by a membrane from the rest of the petrol cut (forming the γ cut), and are evacuated via line 3 to feed an oligomerization unit (C).

The depleted fraction of olefins and linear paraffins is removed from the unit (B) by the line 7. This section called γ cut, whose linear olefin content has significantly decreased since it mainly contains only branched olefins, has a subscript improved octane compared to the initial gasoline cut or α cut.

More specifically, any type of membrane making it possible to effect the separation between paraffins and linear olefins on the one hand, and paraffins and branched olefins on the other hand, can be used, whether organic or polymeric membranes (for example, the Sulzer Chemtech Membrane Systems PDMS 1060 Membrane), Ceramics or (for example at least partly of zeolite, silica, alumina, glass or carbon), or composites consisting of polymer and at least one mineral compound or ceramic (for example, the Sulzer Chemtech Membrane PDMS 1070 membrane Systems).

Many works of literature refer to formed film-based membranes molecular sieves, such as MFI-type zeolites, which make it possible to separate very efficiently paraffins linear branched paraffins through a mechanism of diffusional selectivity.

All types of membranes based on MFI zeolites, be they membranes based of silicalite, based on MFI zeolite completely dealuminated, exhibit a selectivity normal / isoparaffins and can therefore be used in the context of the present invention.

• van de Graaf, J.M., van der Bijl, E., Stol, A., Kapteijn, F., Moulijn, J.A., dans Industrial Engineering Chemistry Research ("Recherche en genie des procédés industriels"), 37, 1998, 4071-4083;
• Gora, L., Nishiyama, N., Jansen, J.C., Kapteijn, F., Teplyakov, V., Maschmeyer, Th., dans Separation Purification Technology ("Technologies de séparation/purification"), 22-23, 2001, 223-229;
• Nishiyama, N., Gora, L., Teplyakov, V., Kapteijn, F., Moulijn, J.A., dans Separation

Among these MFI-type zeolites, mention may be made of those described in the following articles or communications:

• van de Graaf, JM, van der Bijl, E., Stol, A., Kapteijn, F., Moulijn, JA, in Industrial Engineering Chemistry Research , 37, 1998, 4071-4083 ;
• Gora, L., Nishiyama, N., Jansen, JC, Kapteijn, F., Teplyakov, V., Maschmeyer, Th., In Separation Purification Technology ("Separation / Purification Technologies"), 22-23, 2001, 223 -229;
• Nishiyama, N., Gora, L., Teplyakov, V., Kapteijn, F., Moulijn, JA, in Separation

Purification Technology ("Separation / Purification Technologies"), 22-23, 2001, 295-307.

• Coronas, J., Falconer, J.L., Noble, R.D., dans AIChE Journal ("Journal de l'Association de Ingénieurs en Génie des Procédés"), 43, 1997, 1797-1812;
• Gump, C.J., Lin, X., Falconer, J.L., Noble, R.D., dans Journal of Membrane Science ("Journal de la science des membranes"), 173, 2000, 35-52.

Among the native ZSM-5 zeolite membranes, the following communications can be cited:

• Coronas, J., Falconer, JL, Noble, RD, in AIChE Journal ("Journal of the Association of Process Engineering Engineers"), 43, 1997, 1797-1812;
• Gump, CJ, Lin, X., Falconer, JL, Noble, RD, in Journal of Membrane Science , 173, 2000, 35-52.

Finally, among the membranes that have been exchanged with ions of the H +, Na +, K +, Cs +, Ca + or Ba + type, mention may be made of Aoki, K., Tuan, VA, Falconer, JL, Noble, RD, in Microporous Mesoporous Materials ("Materials microporous and mesoporous "), 39, 2000, 485-492.

• 200 à 400 tel que cité dans la publication de Coronas, J., Noble, R.D., Falconer, J.L., dans Industrial Engeneering and Chemical Research ("Recherche en génie des procédés industriels"), 37, 1998, 166-176;
• de 100 à 700 (Gump, C.J., Noble, R.D., Falconer, J.L., dans Industrial Engeneering and Chemical Research ("Recherche en génie des procédés industriels"), 38, 1999,2775-2781;
• de 600 à plus de 2000 (Keizer, K., Burggraaf, A.J., Vroon, Z.A.E.P., Verweij, H., dans

The published values of selectivity n-C4 / i-C4 in mixture, obtained with this type of membrane, vary between 10 and 50 according to the operating conditions. On this point it is possible to consult the publication van de Graaf, JM, van der Bijl, E., Stol, A., Kapteijn, F., Moulijn, JA, in Industrial Engineering Chemistry Research ("Research in engineering of industrial processes") , 37, 1998, 4071-4083.
The separation selectivities observed with membranes based on MFI zeolites applied to the separation n-hexane / dimethylbutane are even higher:

• 200 to 400 as cited in the publication of Coronas, J., Noble, RD, Falconer, JL, in Industrial Engeneering and Chemical Research ("Industrial Process Engineering Research"), 37, 1998, 166-176;
• from 100 to 700 (Gump, CJ, Noble, RD, Falconer, JL, in Industrial Engeneering and Chemical Research, 38, 1999 , 2775-2781;
• from 600 to over 2000 (Keizer, K., Burggraaf, AJ, Vroon, ZAEP, Verweij, H., in

Journal of Membrane Science , 147, 1998, 159-172.

The selectivity of this type of membrane is essentially based on a difference in diffusivity between linear compounds, diffusing faster because offering a diameter significantly lower kinetics than the micropore diameter of the zeolite, and the connected compounds, diffusing more slowly because having a kinetic diameter close to that of micropores.

Paraffins and their branched or linear olefinic homologues having a diameter very close kinetics, the MFI zeolite-based membranes finally offer normal selectivities / high iso olefins, close to those observed for normal / iso paraffins under similar operating conditions.

It is also possible to envisage using zeolite membranes of structural type LTA, zeolite which has a very good form selectivity with respect to normal paraffins.

The operating temperature of the membrane will be between the temperature ambient temperature and 400 ° C, and preferably between 80 ° C and 300 ° C.

The linear olefins and paraffins (β-section) separated from the petrol fraction in unit B, are sent to an oligomerization reactor, represented by unit C, by via line 3.

This unit C contains an acid catalyst. The hydrocarbons present in the mixture of paraffins and linear olefins will undergo moderate oligomerization reactions, this is to say in general dimerizations or trimerizations, the conditions of the reaction being optimized for the production of a majority of hydrocarbons with carbon numbers is predominantly between 9 and 25, and preferably between 10 and 20.

The catalyst of unit C can be chosen from the group formed by silicoaluminates, titanosilicates, mixed titanium alumina, clays, resins, mixed oxides obtained by grafting at least one organometallic, organosoluble or water-soluble compound (selected from the group consisting of alkys and / or alkoxy metals having at least one such as titanium, zirconium silicon, germanium, tin, tantalum, niobium) on an oxide support such as alumina (gamma, delta, eta forms, alone or in mixture), silica, silica aluminas, titanium silicas, zirconia silicas, or any other solid having any acidity.

Preferably, the catalyst used to carry out the oligomerization comprises at least a metal of group VIB of the periodic table, and advantageously an oxide of said metal. Said catalyst may further comprise an oxide support selected from the group formed by aluminas, titanates, silicas, zirconia, alumino-silicates.

A particular embodiment of the invention consists in implementing a mixture of at least two of the catalysts mentioned above.

The pressure of the unit C is most often such that the charge is in liquid form. This pressure is in principle between 0.2 MPa and 10 MPa, preferably between 0.3 and 6 MPa, and more preferably between 0.3 and 4 MPa. The volume flow ratio of load on the catalyst volume (also called hourly volume velocity or VVH) can be between 0.05 liter / liter.hour and 50 liters / liter.hour, preferably between 0.1 liter / liter.hour and 20 liters / liter.hour, and even more preferably between 0.2 liter / liter.hour and 10 liters / liter.hour.

It was found by the plaintiff that under pressure and VVH conditions above, the reaction temperature should have been between 15 ° C and 300 ° C, preferably between 60 ° C and 250 ° C, and more particularly between 100 ° C and 250 ° C for optimize the quality of the products obtained.

The effluent from the unit (C) is then sent via line 4 in one or several distillation columns shown in the diagram of Figure 1 by the unit (D).

• une coupe δ dite légère dont le point final de distillation est compris entre environ 150°C et environ 200°C, de préférence entre 150°C et 180°C.
• une coupe η dite lourde dont le point initial d'ébullition est compris entre environ 150°C et environ 200°C, de préférence entre 150°C et 180°C. Cette coupe est transportée par la ligne 6 vers l'unité (E).

La coupe lourde η est une coupe dont le point initial correspond une coupe gazole.The unit (D) may also consist of a flash balloon or any other means known to those skilled in the art for separating the effluents in at least two distinct sections by their boiling point:

• a so-called light cup whose final distillation point is between about 150 ° C. and about 200 ° C., preferably between 150 ° C. and 180 ° C.
• a so-called heavy section whose initial boiling point is between about 150 ° C and about 200 ° C, preferably between 150 ° C and 180 ° C. This section is transported by line 6 to the unit (E).

The heavy cut η is a section whose initial point corresponds to a diesel cut.

This cut consists mainly of olefins and diolefins resulting from the polymerization of linear olefins. This cup can be hydrogenated in a unit conventional hydrogenation in the presence of a catalyst and under operating conditions well known to those skilled in the art. These olefins are then converted into paraffins linear. The effluent of the hydrogenation unit (E) is a cetane gas oil greater than 45 and preferably greater than 50.

The δ cut consists mainly of non-reactive linear paraffins during the oligomerization reaction. This cut, conveyed by line 5, is mixed with the hydrogen, conveyed via line 10, is injected into a dehydrogenation unit (F). Water or any other compound likely to decompose into water under the conditions of dehydrogenation may be added to the charge. The amount of water present in the load hydrocarbons, (this water may be generated by the decomposition of another compound, as for example an alcohol, an aldehyde, a ketone, an ether), will be between 1 and 10000 ppm weight of water relative to the hydrocarbon charge.

The dehydrogenation unit (F) operates under temperature conditions between 400 ° C and 520 ° C, preferably between 450 ° C and 490 ° C.

The pressures of the dehydrogenation unit (F) are between 0.05 MPa and 1 MPa, preferably between 0.1 MPa and 0.5 MPa.

The ratio of the volume flow rate of the feedstock to the catalyst volume is between 1 h ^-1 and 500 h ^-1 , preferably between 15 h ^-1 and 300 h ^-1 . The molar ratio of hydrogen to hydrocarbon is between 1 and 20 mol / mol, and preferably between 4 and 12 mol / mol.

The dehydrogenation catalyst of the unit (F) may be chosen from catalysts known to those skilled in the art for the dehydrogenation of short paraffins ranging from C 2 to C 5 or long paraffins ranging from C 10 to C 14. The catalyst thus consists of a metal phase supported on a support whose specific surface is advantageously between 5 and 300 m ² / g.

This catalyst support comprises at least one refractory oxide which is generally selected from the group IIA, IIIA, IIIB, IVA or IVB metal oxides of the periodic classification of elements such as, for example, magnesium oxides, aluminum, silicon, zirconium alone or mixed with each other, or as a mixture with oxides of other elements of the Periodic Table. We can also use the coal.

a) au moins un métal du groupe VIII choisi parmi l'iridium, le nickel, le palladium, le platine, le rhodium et le ruthénium. Le platine sera généralement le métal préféré. Le pourcentage pondéral est choisi entre 0,01 et 5%, et de préférence entre 0,02 et 1 %.

b) au moins un élément additionnel choisi dans le groupe constitué par le germanium, l'étain, le plomb, le rhénium, le gallium, le fer, l'indium et le thallium. Le pourcentage pondéral est choisi entre 0,01% et 10%, et de préférence entre 0,02% et 5%. On peut avantageusement dans certains cas utiliser à la fois au moins deux des métaux de ce groupe.

The catalyst of the dehydrogenation unit (F) contains in addition to this support:

a) at least one Group VIII metal selected from iridium, nickel, palladium, platinum, rhodium and ruthenium. Platinum will usually be the preferred metal. The weight percentage is chosen between 0.01 and 5%, and preferably between 0.02 and 1%.

b) at least one additional element selected from the group consisting of germanium, tin, lead, rhenium, gallium, iron, indium and thallium. The weight percentage is chosen between 0.01% and 10%, and preferably between 0.02% and 5%. In some cases, it is advantageous to use at least two of the metals of this group.

Optionally, the dehydrogenation catalyst of the unit (F) may also contain a sulfur compound, at a weight content of sulfur element generally between 0.005 and 1% with respect to the catalyst mass.

The catalyst of the unit (F) may also contain one or more additional elements typically allowing to limit the acidity of the support such as alkaline or alkaline earth, with a weight percentage of 0.01% to 3%.

It may also contain from 0.01% to 3% of a halogen or halogenated compound.

The amounts of these alkaline and / or alkaline earth compounds on the one hand, and halogenated substances, may be adjusted to modify the content of alkylaromatics, and / or branched paraffins formed during the reaction of dehydrogenation.

These compounds are in fact successive products of the dehydrogenation reaction of paraffins processed in this process.

It is known that aromatic compounds as well as branched paraffins have a good better octane number than linear paraffins. Since these products are not affected by the step of selective hydrogenation, their production at the stage of dehydrogenation (F) will enrich the petrol cut (evacuated by line (7)) after the membrane separation step (B).

Thus, the diesel cut will for example be favored by the use of a catalyst of dehydrogenation having from 0.01% to 3% of at least one alkaline and / or alkaline earth metal and less than 0.2% of halogenated compound.

According to a first variant, the proportion of aromatic compounds resulting from this dehydrogenation step may also be minimized by a judicious choice of operating conditions, known to those skilled in the art. The use of a high charge-to-volume ratio (VVH) or a high H2 / HC ratio makes it possible to limit the formation of aromatics during the dehydrogenation step (F). A VVH value of between 15 and 300 h ^-1 , and an H 2 / HC value of between 4 and 12 will generally be preferred.

The petrol cut will for example be favored by the use of a catalyst of dehydrogenation having 0.1% to 3% of a halogenated compound, and less than 0.5% of an alkaline and / or alkaline earth metal. The catalyst may in some cases not contain alkali metal or alkaline earth metal.

According to a second variant, the proportion of aromatic compounds resulting from this dehydrogenation step (F) may also be optimized by a judicious choice of operating conditions, known to those skilled in the art. The use of a low charge-to-volume ratio of catalyst (VVH) makes it possible, for example, to increase the formation of aromatics with respect to the formation of olefins. A VVH value of between 1 and 50 h ^-1 will in this case be generally preferred.

In unit (F), the step of dehydrogenating paraffins to olefins is also accompanied, in addition to branched aromatic and paraffin compounds, diolefin formation and optionally other unsaturated compounds such as alkynes, triolefins.

The formation of diolefins is strongly influenced by the thermodynamic equilibrium between paraffins / olefins / diolefins.

The effluent from the unit (F) discharged via the line (11) is mixed with hydrogen supplied by the line (12) and then sent to a selective hydrogenation unit (G) whose purpose is the elimination by hydrogenation of the small quantities of diolefins and possible alkynes and triolefins, without affecting the olefins and aromatic compounds formed in the unit (F). This selective hydrogenation operates in pressure ranges between 1 MPa and 8 MPa, and preferably between 2 MPa and 6 MPa. The temperature is between 40 ° C and 350 ° C, and preferably between 40 ° C and 250 ° C.

The ratio of the volume flow rate of charge to the volume of catalyst (VVH) is between 0.5 and 10 m ³ / m ³ / hour and preferably between 1 and 5 m ³ / m ³ / hour.

The catalyst of the hydrogenation unit (G) consists of a support based on silica, or of alumina on which is deposited a metal type nickel, platinum or palladium. The catalyst of the hydrogenation unit (G) may also consist of mixtures of nickel and molybdenum or mixtures of nickel and tungsten.

At the end of the selective hydrogenation (G), the effluent of the unit (G) contains mainly linear paraffins, olefins and aromatics. This so-called cup λ cut, is then recycled in whole or in part by the line (13) at the entrance of the unit (B).

Examples:

The following examples illustrate the advantages of the present invention.

Example 1 corresponds to the invention and will be better understood by following FIG.

Example 2 is a comparative example

Example 1 (according to the invention)

In this example, the load is a FCC gasoline with a boiling point between 40 ° C and 150 ° C. This gasoline contains 10 ppm nitrogen.

This charge is sent to a purification reactor A containing a solid a mixture of 20% alumina and 80% by weight of zeolite of the mordenite type. The zeolite used in the present example has a silicon / aluminum ratio of 45.

The pressure of the purification unit is 0.2 MPa.

The ratio of the liquid volume flow rate of the charge to the acid solid volume (VVH) is of 1 liter / liter.hour. The temperature of the reactor is 20 ° C.

Table 1 gives the composition of the initial charge and that of the effluent from unit A (α cut). The charge rate used is 1 kg / h. characteristics of the charge and effluent of unit A. Charge A Effluent of unit A Nitrogen (ppm) 10 0.2 Paraffins (% wt) 25.2 25.1 Naphthenes (% wt) 9.6 9.8 Aromatic (% by weight) 34.9 35 Olefins (% by weight) 30.3 30.1

The effluent from unit A (α cut) is then sent to a membrane reactor B consisting of a support based on α-alumina on which is deposited a layer of zeolite MFI with a thickness of between 5 and 15 μm.

The pressure of the membrane reactor B is equal to 0.1 MPa and the temperature is equal to 150 ° C.

Table 2 gives the composition of effluents from unit B (β cut and γ cut). effluent characteristics of stage B (before recycling). Β cut Γ cup Yield (%) (relative to the α cut) 8.8 91.2 Production (g / h) 88 912 Paraffins (% wt) 45.5 23.1 Naphthenes (% wt) 10.7 Aromatic (% by weight) 38.5 Olefins (% by weight) 54.5 27.7

The β cut from the membrane separation unit is injected into an oligomerization reactor (C) containing a catalyst consisting of a mixture of 50% by weight of zirconia and 50% by weight of H ₃ PW ₁₂ O ₄₀ .

The pressure of the unit is 2 MPa, the ratio of the volumetric load flow on the volume of catalyst (VVH) is equal to 1.5 liters / liter.hour. The temperature is set at 170 ° C.

At the outlet of the reactor of the oligomerization unit (C), an effluent is obtained which is then separated into two sections by means of a distillation column (D): a light cut δ, and a heavy cut η whose compositions and yields are given in Table 3 below: Production and composition of δ and η sections Cup δ Cup η Production (g / h) 39.6 48 Paraffins (%) 100 Olefins (%) 100

The heavy cut η is sent to a hydrogenation reactor (E) containing a catalyst comprising an alumina support on which nickel and molybdenum (marketed by AXENS under the trade name HR348, brand Mark).

The pressure of the unit is 5 MPa, the ratio of the volumetric load flow on the volume of catalyst (VVH) is equal to 2 liters / liter.hour.

The ratio of the injected hydrogen flow rate to the feed rate is equal to 600 liters / liter.

The reactor temperature is 320 ° C.

The characteristics of the effluent from step (E) which are those of a diesel fuel, are presented in Table 4. characteristics of effluent from unit E effluent from unit E Density at 20 ° C (kg / l) 0.787 Sulfur (ppm) 1 Cetane engine 55

The light cut δ distillation range 40 ° C-200 ° C from the distillation step (D), is mixed with hydrogen with a hydrogen to hydrocarbon molar ratio of 6 moles / mole, then sent to the dehydrogenation unit (F).

The total pressure of the dehydrogenation unit (F) is equal to 0.3 MPa, and the temperature is 475 ° C. The ratio of the volume flow rate of charge to the volume of catalyst (VVH) is equal to 20 liters / liter.hour. The catalyst used in the dehydrogenation unit (F) is sold by AXENS under the reference DP 805, registered trademark.

The composition of the section μ resulting from the dehydrogenation (F) or μ section is presented in Table 5 and compared to the charge of the dehydrogenation unit (F) or cut δ. characteristics of the effluent from unit F (μ section) Cup δ Μ section Linear paraffins (% by weight) 100 85.1 Branched paraffins (% by weight) 0.3 Olefins (% by weight) 12 Aromatic (%) 2 Diolefins (% by weight) 0.6

This section μ is mixed with hydrogen and sent to a reactor hydrogenation product (G) containing a catalyst marketed by AXENS under the reference LD 265, registered trademark.

The pressure of the unit is 2.8 MPa, the temperature is equal to 90 ° C, and the flow ratio The volume of charge on the volume of catalyst (VVH) is equal to 3 liters / liter / hour.

The composition of the λ-section resulting from this selective hydrogenation (G) is compared with that of the μ-section in Table 6. characteristics of the effluent from unit G (λ cut) Μ section Λ cut Linear paraffins (% by weight) 85.1 85.2 Branched paraffins (% by weight) 0.3 0.3 Olefins (% by weight) 12 12.5 Aromatic (%) 2 2 Diolefins (% by weight) 0.6 0

This section λ is completely recycled at the entrance of the membrane reactor (B).

Paraffins and linear olefins are thus found in the new β-section obtained after recycling and thereby increase the diesel yield.

The properties of the γ cut thus obtained are presented in Table 6 and compared with those of the initial cut α. Comparison of the characteristics of the initial cut α and the final cut γ. Α cut Final γ cup Paraffins (% wt) 25.2 22.9 Naphthenes (% wt) 9.6 10.4 Aromatic (% by weight) 34.9 37.8 Olefins (% by weight) 30.3 27.6 RON octane number 92 97

The present method makes it possible to obtain, from a petrol cut from an FCC, a cut gasoline (γ cut) with an improved octane number compared to that of the cut initial (97 against 92) and a diesel cut, effluent of the unit (E), with high cetane number (55), perfectly compatible with marketing to European specifications and US.

Example 2 (comparative)

Example 2 corresponds to the prior art and consists in sending directly to a unit of oligomerization (C) a gasoline fraction of FCC (α cut) whose boiling point is between 40 ° C and 150 ° C.

This gasoline contains 10 ppm nitrogen.

This charge is sent to a purification reactor A containing a solid a mixture of 20% alumina and 80% by weight of zeolite of the mordenite type. The zeolite used in the present example has a silicon / aluminum ratio of 45.

The pressure of the purification unit is 0.2 MPa.

The ratio of the liquid volume flow rate of the charge to the acid solid volume (VVH) is of 1 liter / liter.hour. The temperature of the reactor is 20 ° C.

Table 7 gives the composition of the initial charge and that of the effluent from unit A. The charge rate used is 1 kg / h. characteristics of the charge and effluent of unit A. Charge A Effluent of unit A Nitrogen (ppm) 10 0.2 Paraffins (% wt) 25.2 25.1 Naphthenes (% wt) 9.6 9.8 Aromatic (% by weight) 34.9 35 Olefins (% by weight) 30.3 30.1

The effluent from unit A (α cut) is sent to an oligomerization unit (C) working under the conditions described in Example 1.

• une coupe légère δ' d'intervalle de distillation 40°C-200°C obtenue avec un rendement poids de 70%,
• une coupe lourde η' comprenant les hydrocarbures dont le point de distillation initial est supérieur à 200°C, obtenue avec un rendement poids de 30%.

At the end of the oligomerization step (C), the effluent from the oligomerization unit (C) is separated into 2 sections by means of the distillation column (D):

• a light cut δ 'distillation range 40 ° C-200 ° C obtained with a weight yield of 70%,
• a heavy cut η 'comprising hydrocarbons whose initial distillation point is greater than 200 ° C, obtained with a weight yield of 30%.

The heavy cut η 'is sent to a hydrogenation reactor (E) containing a Alumina catalyst on which nickel and molybdenum are deposited.

The pressure of the unit (E) is 5 MPa, the ratio of the flow rate of charge on the catalyst volume (VVH) is equal to 2 liters / liter.hour. The ratio of hydrogen flow injected on the charge flow is equal to 600 liters / liter.

The reactor temperature of the unit (E) is 320 ° C. The characteristics of the effluent from the unit (E) which are those of a diesel fuel, are presented in Table 8. characteristics of the effluent from unit E Effluent of unit E Density at 20 ° C (kg / l) 0.787 Sulfur (ppm) 1 Motor cetane index 35

It is found that the cetane number of the gas oil obtained when the oligomerization is carried out without first separating the linear compounds from the branched compounds is clearly less than that obtained from Example 1 according to the invention.

The gas oil obtained according to the scheme of Example 2 is unfit for marketing, which is not the case of that obtained in Example 1 according to the invention.

Likewise, the final gasoline cut δ 'has an octane number of 85, lower than obtained in Example 1, which can make marketing problematic.

The properties of this essence cut δ 'are compared with those of the initial gasoline cut (α cut) in Table 9 below. characteristics of cuts α and δ ' Α cut Cup δ ' Production (g / l) 1000 700 Paraffins (% wt) 25.2 36.2 Naphthenes (% wt) 9.6 13.7 Aromatic (% by weight) 34.9 50.1 Olefins (% by weight) 30.3 RON octane number 92 85

Claims (13)

Process for the conversion of a hydrocarbon feedstock of the gasoline type, comprising from 4 to 15 carbon atoms, into a petrol fraction with an octane number greater than that of the feedstock and a gas oil fraction with a cetane number greater than 45, said process comprising the following steps: a) a membrane separation step (B) of the hydrocarbon feedstock under conditions allowing the selective separation of the majority of linear olefins present in said feedstock and constituting the β-cut, the cut containing the majority of branched olefins, called γ-cut; , constituting a gasoline with a high octane number, higher than that of the charge. b) an oligomerization step (C) of the linear olefins (β-cut) contained in the effluents resulting from the membrane separation step (B) under moderate oligomerization conditions, c) a step of separation by distillation (D) of the effluents resulting from the oligomerization step in at least two sections: a section δ comprising the hydrocarbons whose final boiling point is below a temperature of between 150 ° C. and 200 ° C., a fraction η comprising hydrocarbons whose initial boiling point is greater than a temperature of between 150 ° C. and 200 ° C., d) a hydrogenation step (E) of the cut η making it possible to obtain a gas oil with a cetane number of at least 45. The method of claim 1 further comprising after step d) a step e) of dehydrogenation (F) of the section δ making it possible to convert at least part of the paraffins to olefins, and producing a μ-cut which is, at least in part, recycled to the membrane separation step (B). The method of claim 2 wherein the section μ from the step of dehydrogenation (F) undergoes selective hydrogenation (G), in order to eliminate diolefins so as to produce a cut λ which is recycled at least in part to the stage membrane separation (B). The method of claim 2 wherein the section μ from the step of dehydrogenation (F) of the δ cut, is mixed at least in part with the γ cut, of the membrane separation unit (B). Process according to claim 3, in which the λ cut resulting from the hydrogenation step selective (G) is at least partially mixed with the γ cut, resulting from the separation step by membrane (B). A process according to any one of claims 1 to 5 wherein the step oligomerization (C) is carried out at a pressure of between 0.2 and 10 MPa, a ratio of volume flow rate of charge on catalyst volume (VVH) between 0.05 liter / liter.hour and 50 liters / liter.hour, a temperature between 15 ° C and 300 ° C, and in presence of a catalyst comprising at least one metal of group VIB of the classification periodic. Process according to one of Claims 1 to 6, in which the separation step on membrane is made with a membrane such as those used in nanofiltration or reverse osmosis, or permeation in the gas phase, or pervaporation. Process according to any one of claims 1 to 6 wherein the separation unit by membrane uses a film-based membrane formed from molecular sieve type silicates, aluminosilicates, aluminophosphates, silicoaluminophosphates, metalloaluminophosphates, stanosilicates or a mixture of at least one of these two types of constituents. Process according to any one of claims 1 to 6 wherein the separation unit by membrane uses a membrane based on zeolites of type MFI or ZSM-5, native or having been exchanged with H + ions; Na +; K +; Cs +; Ca +; Ba +. A process according to any one of claims 1 to 6 wherein the unit of membrane separation uses a membrane based on LTA type zeolites. Process according to any one of claims 1 to 10 wherein the catalyst of dehydrogenation of the unit (F) consists of a metallic phase deposited on a support, this support comprising at least one refractory oxide selected from oxides of metals of groups IIA, IIIA, IIIB, IVA or IVB of the periodic table of elements. Process according to any one of claims 1 to 11 wherein the catalyst of the unit (F) contains one or more additional elements selected from alkalis or alkaline earth, with a weight percentage of between 0.01% and 3%. Process according to any one of claims 1 to 12 comprising a step (A) removal of at least a portion of the nitrogenous or basic impurities contained in the hydrocarbon feedstock, this step (A) being located upstream of the feed unit membrane separation (B).

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