EP1602705B1 - Process for upgrading a gasoline fraction and transforming in gasoils with additional treatment for increasing the efficiency of the gasoil fraction - Google Patents

Description

Field of the invention

The present invention relates to a method allowing a simple and economical way to modulate the respective productions of gasoline and diesel. More precisely, according to the process that is the subject of the present application, it is possible to convert an initial hydrocarbon feedstock in the gasoline cut, comprising from 4 to 15 carbon atoms and preferably from 4 to 11 carbon atoms, into a gasoline fraction of improved octane number with respect to the charge, and a gas oil fraction with a high cetane number.

The present application constitutes an improvement of the application entitled "Process for improving gasoline cuts and conversion to gas oils" by the same inventors and filed on the same day as the present application.

The effects of this improvement relate to the efficiency of the gasoil fraction obtained, to the octane number of the gasoline fraction obtained, and finally to the fact that the starting gasoline fraction can be of absolutely any composition while respecting only the range of number of carbon atoms.

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

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

1. a) branched olefins which have good octane numbers. This octane number increases with the number of branches and decreases with the length of chain.
2. b) linear olefins which have a low octane number, this octane number decreasing strongly with the chain length.

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 gas oil cut of cetane number at least equal to 45 and preferably greater than 50.

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

These effluents are used in the composition of commercial species at a rate of 20 to 40% depending on the geographical origin (27% in Western Europe and 36% in the USA).

It is likely that in the context of environmental protection, the standards for commercial species will be directed in the coming years towards a reduction in the content of olefins allowed in gasolines.

It follows from the foregoing points that the production of gasolines with low olefins but maintaining an acceptable octane number can be achieved only by selecting olefins for gasoline, exclusively or in very large proportions. branched with high octane number.

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

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

More specifically, the use of the present process may advantageously make it possible to 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 converting 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 hydrocarbon feedstocks), solvent-soluble catalysts ( EP 0714871 ) or heterogeneous catalysts ( US 4,956,518 ).

By way of example, the processes for adding isobutane to 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 indices. octane.

Other transformations using etherification methods of branched olefins, such as for example those described in US Pat. US Patents 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 having between 2 and 4 carbon atoms, allow the production of gasoline cuts or distillates. An example of such a method is described in 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 they are produced under conditions favoring the formation of heavier cuts, they generate gasoil cuts with a very low cetane number.

Such examples are further illustrated by the US Patent 4,456,779 and US 4,211,640 .

The US Patent 5,382,705 proposes to couple the oligomerization and etherification processes previously described in order to produce, from a C ₄ fraction, tertiary alkyl ethers such as MTBE or ETBE and lubricants.

Finally the patent US 2003/0171632 A1 describes a process for producing a gas oil fraction from an olefinic feedstock comprising branched olefins with a number of carbon atoms between 3 and 8, by bringing said feedstock into contact with a zeolite type acid catalyst with a selectivity of form, at high temperature and under pressure, so as to obtain longer olefins. This patent does not describe any prior separation of normal and iso paraffins.

The patent US 2004/0033370 A1 describes a zeolite membrane deposited on a support and having given permeation and selectivity performances measured on the separation of normal and isobutane. This patent cites an application to the separation of normal and isoolefins, but does not describe any process for the production of a gas oil and the production of gasoline with an improved octane number relative to the feedstock.

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 distillation separation stage and comprising the majority of linear paraffins and a part of linear olefins, is directly introduced into a catalytic reforming unit of the gasolines that is supposed to exist on the site of production.

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

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

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 of charge on catalyst volume (called VVH) of between 0.degree. , 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 on the one hand, and branched olefins and paraffins, on the other hand, is carried out in a so-called membrane separation unit which can use a very wide variety of membrane types. 'being in no way related to a particular type of membrane.

The membranes which may be used in the context of the invention are preferably membranes used in nanofiltration and in reverse osmosis (membranes falling within the category of membranes for filtration processes) or membranes used in permeation in the gas phase or in pervaporation ( membrane falling within the category of membranes for permeation processes).

From the material point of view, these membranes may be either zeolite type membranes, or polymer (or organic) type membranes, or ceramic (or mineral) type membranes, or even 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 that is the subject of the invention may also be based on film. For example, there may be mentioned in the latter category the membranes based on film formed by molecular sieves, or film-based membranes formed from molecular sieves of silicates, aluminosilicates, aluminophosphates, silicoaluminophosphates, metalloaluminophosphates, stanosilicates, or a mixing at least one of these two types of constituents.

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

In some cases, the process according to the invention may comprise a step of removing at least a portion of the nitrogenous or basic impurities contained in the initial charge of hydrocarbons.

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

Detailed description of the invention

The invention will be better understood on reading the figure 1 which corresponds to the process diagram according to the invention and in which the optional units have been indicated in dashed lines, the other units in solid lines being compulsory.

According to figure 1 the hydrocarbon feedstock is conveyed via line 1 to a purification unit A.

This unit A eliminates a large part of the nitrogen compounds and / or basic contained in the load. This removal, although optional, is necessary when the feedstock comprises a high level of nitrogen and / or basic compounds, as these constitute a poison for the catalysts of the subsequent steps of the present process.

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

The solid may also be chosen from mixed oxides obtained by grafting at least one 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 (gamma, delta, eta, alone or as a mixture), silica, silica aluminas, titanium silicas, zirconia silicas, resins ion exchange type Amberlyst, or any other solid having any acidity.

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

The pressure of the purification unit (A) of the charge is between atmospheric pressure and 10 MPa, preferably between atmospheric pressure and 5 MPa, and a pressure under which the charge is located is preferably chosen. 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 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 elimination 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 membrane separation unit (B). In unit (B), the linear olefins and paraffins forming the β-section are separated by a membrane from the remainder of the gasoline cut (forming the γ-section), and are discharged via line 3 to feed an oligomerization unit. (VS).

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

More specifically, any type of membrane that makes it possible to carry out 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 PDMS 1060 membrane of Sulzer Chemtech Membrane Systems), ceramics or minerals (composed for example at least partly of zeolite, silica, alumina, glass or carbon), or composites consisting of polymer and at least one mineral or ceramic compound (eg, Sulzer Chemtech Membrane Systems PDMS 1070 membrane).

Numerous works in the literature refer to molecular sieve film-based membranes, such as MFI-type zeolites, which make it possible to very efficiently separate linear paraffins from branched paraffins by means of a diffusional selectivity mechanism.

All types of membrane based on MFI zeolites, whether silicalite membranes based on MFI zerolite completely dealuminated, have a normal selectivity / 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 Engineers in Process Engineering"), 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 ("Microporous and Mesoporous Materials"), 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 we can 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 quoted 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 the linear compounds, diffusing faster because offering a kinetic diameter substantially smaller than the micropore diameter of the zeolite, and the connected compounds, diffusing more slowly because having a kinetic diameter close to that of the micropores.

Since paraffins and their branched or linear olefinic homologues have a very close kinetic diameter, the MFI zeolite membranes finally provide high normal / isoolefin selectivities, close to those observed for normal / iso paraffins under similar operating conditions.

It is also possible to envisage the use of membranes based on zeolite 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 room 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, 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, ie in general dimerizations or trimerizations, the conditions of the reaction being optimized for the production of a majority of hydrocarbons whose carbon number is mainly between 9 and 25, and preferably between 10 and 20.

The catalyst of unit C may be chosen from the group formed by silicoaluminates, titanosilicates, mixed titanium alumina, clays, resins, mixed oxides obtained by grafting at least one organometallic compound, organosoluble or water-soluble ( selected from the group consisting of alkys and / or alkoxides, metals having at least one element such as titanium, zirconium silicon, germanium, tin, tantalum, niobium) on an oxide support such as alumina (gamma, delta, eta, alone or in admixture), 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 one Group VIB metal of the periodic classification, and advantageously an oxide of said metal. Said catalyst may further comprise an oxide support selected from the group consisting of aluminas, titanates, silicas, zirconias, aluminosilicates.

A particular embodiment of the invention consists in using a physical 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 ratio of the volume flow rate of charge to the volume of catalyst (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 still more preferably between 0.2 liter / liter.hour and 10 liters / liter.hour.

It has been found by the Applicant that, under the prevailing pressure and VVH conditions, the reaction temperature should be between 15 ° C and 300 ° C, preferably between 60 ° C and 250 ° C, and more particularly between 100 ° C and 250 ° C to optimize the quality of the products obtained.

The effluent from the unit (C) is then sent via line 4 into one or more distillation columns shown in the diagram of the 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 section can be hydrogenated in a conventional hydrogenation unit in the presence of a catalyst and under operating conditions that are well known to those skilled in the art. These olefins are then converted to linear paraffins. The effluent of the hydrogenation unit (E) constitutes a gas oil with a cetane number 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 via line 5, is mixed with hydrogen, conveyed via line 10, is injected into a dehydrogenation unit (F). Water or any other compound capable of decomposing into water under the dehydrogenation conditions may be added to the load. The amount of water present in the hydrocarbon feedstock, (this water may be generated by the decomposition of another compound, such 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 at temperatures of 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 chosen from metal oxides of groups IIA, IIIA, IIIB, IVA or IVB of the periodic table of elements such as, for example, oxides of magnesium, aluminum, silicon, zirconium taken alone or mixed with each other, or mixed with oxides of other elements of the periodic table. We can also use coal.

1. 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 %.
2. 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:

1. 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%.
2. 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% relative to the catalyst mass.

The catalyst of the unit (F) may also contain one or more additional elements which conventionally make it possible to limit the acidity of the support, such as alkaline or alkaline-earth metals, 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 compounds, on the other, may be adjusted so as to modify the content of compounds alkylaromatics, and / or branched paraffins formed during the dehydrogenation reaction.

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

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

Thus, for example, the diesel fraction will be favored by the use of a dehydrogenation catalyst 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 gasoline cut will for example be favored by the use of a dehydrogenation catalyst having from 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 certain cases not contain an 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 the unit (F), the dehydrogenation step of paraffins to olefins is also accompanied, in addition to branched aromatic and paraffin compounds, the formation of diolefins and possibly 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) evacuated via the line (11) is mixed with hydrogen brought by the line (12) and then sent to a selective hydrogenation unit (G) whose purpose is elimination by hydrogenation of small amounts of diolefins and possible alkynes and triolefins, without affecting the olefins and aromatic compounds formed in unit (F). This selective hydrogenation operates in pressure ranges of 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 alumina on which is deposited a nickel, platinum or palladium type metal. 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 cut called λ cut, is then recycled all 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 the figure 1 .

Example 2 is a comparative example

Example 1 (according to the invention)

In this example, the feedstock is a FCC gasoline 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 consisting of 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 volume of acid solid (VVH) is 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. Table 1: Load and effluent characteristics 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 MFI zeolite 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). Table 2: characteristics of the effluents 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 volume flow rate of charge 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: Table 3: 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 are deposited nickel and molybdenum (marketed by AXENS under the trade name HR348, registered trademark).

The pressure of the unit is 5 MPa, the ratio of the volume flow rate of charge 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. Table 4: Characteristics of the effluent from unit E effluent from unit E Density at 20 ° C (kg / l) 0.787 Sulfur (ppm) 1 Cetane engine 55

The light fraction δ of the distillation range 40 ° C. to 200 ° C. resulting from the distillation step (D) is mixed with hydrogen with a molar ratio of hydrogen to hydrocarbon of 6 mol / mol and then sent to the dehydrogenation unit (F).

The total pressure of the dehydrogenation unit (F) is 0.3 MPa, and the temperature is 475 ° C. The ratio of the volume flow rate of charge on the volume of catalyst (VVH) is equal to 20 liters / liter / hour. The catalyst used in the dehydrogenation unit (F) is marketed 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. Table 4: 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 hydrogenation reactor (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 ratio of the volume flow rate 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. Table 5: 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. Table 6: 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 gasoline cutoff resulting from an FCC, a gasoline cut (γ cut) having an improved octane number relative to that of the initial cut (97 against 92) and a cut diesel, effluent from the unit (E), with a high cetane number (55), perfectly compatible with marketing to European and US specifications.

Example 2 (comparative)

Example 2 corresponds to the prior art and consists in sending directly to an oligomerization unit (C) an FCC gasoline cut (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 consisting of 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 volume of acid solid (VVH) is 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. Table 7: Characteristics of the charge and the 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 an alumina catalyst on which nickel and molybdenum are deposited.

The pressure of the unit (E) is 5 MPa, the ratio of the volume flow rate of charge 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 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. 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 of the branched compounds is significantly lower than that obtained in 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.

Similarly, the final gasoline cut δ 'has an octane number of 85, lower than that 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. Table 9: Characteristics of the α and δ sections 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 (12)

1. Process for conversion of a gasoline-range hydrocarbon feed, comprising 4 to 15 carbon atoms, into a gasoline fraction with a higher octane rating than that of the feedstream and a gasoil fraction with a cetane number higher than 45, the process including the following steps:

   a) a membrane separation step (B) applied to the hydrocarbon feed under conditions enabling selective separation of the majority of the linear olefins present in said feed and constituting the β fraction, the fraction containing the majority of the branched olefins, termed γ fraction constituting a gasoline with a high octane rating, greater than that of the feed,

   b) an oligomerisation step (C) applied to the linear olefins (β fraction) contained in the effluent from the membrane separation step (B) under moderate oligomerisation conditions,

   c) a distillation separation step (D) applied to the effluent arising from the oligomerisation step in at least two fractions:

   - a δ fraction including hydrocarbons whose end boiling point is below a temperature between 150°C and 200°C,

   - a η fraction including hydrocarbons whose initial boiling point is above a temperature between 150°C and 200°C,

   d) a hydrogenation step (E) applied to the η fraction to obtain a gasoil with a cetane number at least equal to 45,

   e) a dehydrogenation step (F) applied to the δ fraction allowing to convert at least a part of the paraffins into olefins and producing a µ fraction which is, at least partially, recycled to the membrane separation step (B).
2. Process according to Claim 1, wherein the µ fraction arising from the dehydrogenation step (F) undergoes selective hydrogenation (G) to remove the diolefins so as to produce a λ fraction which is recycled, at least partially, to the membrane separation step (B).
3. Process according to Claim 1, wherein the µ fraction arising from the dehydrogenation step (F) applied to the δ fraction is mixed, at least partially, with the γ fraction arising from the membrane separation unit (B).
4. Process according to Claim 2, wherein the λ fraction arising from the selective hydrogenation step (G) is, at least partially, mixed with the γ fraction arising from the membrane separation step (B).
5. Process according to any one of Claims 1 to 4, wherein the oligomerisation step (C) is conducted at a pressure between 0.2 and 10 MPa, with a volume ratio of feed flowrate to catalyst volume (HSV) between 0.05 and 50 litres/litre-hour, and at a temperature between 15°C and 300°C, and in the presence of a catalyst including at least one metal in group VIB of the periodic table.
6. Process according to any one of Claims 1 to 5, wherein the membrane separation step is conducted with a membrane such as those used in nanofiltration or reverse osmosis, or gas phase permeation, or pervaporation processes.
7. Process according to any one of Claims 1 to 5, wherein the membrane separation unit uses a film-based membrane formed from molecular sieves based on silicates, aluminosilicates, aluminophosphates, silicoalumino-phosphates, metallo-aluminophosphates, stanosilicates or a mixture of at least one of these two types of constituents.
8. Process according to any one of Claims 1 to 5, wherein the membrane separation unit uses a membrane based on MFI or ZSM-5 type zeolite, in native form or subjected to ion exchange with H+; Na+; K+; Cs+; Ca+; Ba+ ions.
9. Process according to any one of Claims 1 to 5, wherein the membrane separation unit uses a membrane based on type LTA zeolites.
10. Process according to any one of Claims 1 to 9, wherein the dehydrogenation catalyst in unit (F) is composed of a metallic phase deposited on a support, this support including at least one refractory oxide chosen from the metal oxides in groups IIA, IIIA, IIIB, IVA or IVB of the periodic table of elements.
11. Process according to any one of Claims 1 to 10 wherein the catalyst for unit (F) contains one or more additional elements chosen from the alkalines or alkaline-earths, with a percentage by weight between 0.01% and 3%.
12. Process according to any one of Claims 1 to 11 including a step (A) for the removal of at least part of the nitrogenous or basic impurities contained in the initial hydrocarbon feed, this step (A) being located upstream of membrane separation unit (B).

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