EP1640435A1 - Process of isomerisation of a C7 cut with coproduction of an aromatic cut comprising mainly toluene - Google Patents

Abstract

Preparation of an isomerate (I) (having research octane number of 80) and coproduction of an aromatic fraction (F) (comprising mainly toluene) from a fraction, comprises: using an aromatic (contained in the charge) extraction unit (E), isomerization unit (U) and separation unit (S) for linear and mono-, di- and tribranched paraffin, where (I) contains less than 1 (preferably 0.5) wt.% of aromatics. Preparation of an isomerate (I) (having research octane number of 80) and coproduction of an aromatic fraction (F) (comprising mainly toluene) from a fraction (comprising hydrocarbons (with 7 carbon atoms) containing paraffin, naphthenes and aromatics), comprises: using an aromatic (contained in the charge) extraction unit (E), isomerization unit (U) and separation unit (S) for linear and mono-, di- and tribranched paraffin, where (I) contains less than 1 (preferably 0.5) wt.% of aromatics.

Description

Field of the invention

The suppression of lead alkyls in automotive gasolines and more recently the limitation of aromatic content in gasolines (35% in 2005 against 42% currently) has led to a development of branched paraffin production processes which have a much better index octane than linear paraffins, and in particular the process for isomerizing normal paraffins into branched paraffins.

This process is becoming increasingly important in the oil industry.

• un naphta léger (coupe C₅-C₆) qui est envoyé à l'isomérisation,
• un naphta lourd (coupe C₇-C₁₀) qui est envoyé au reformage catalytique.

The current valorization schemes for naphtha (C ₅ -C ₁₀ cut) resulting from the atmospheric distillation of petroleum most often include a fractionation producing:

• a light naphtha (C ₅ -C ₆ cut) which is sent to isomerization,
• a heavy naphtha (C ₇ -C ₁₀ cut) which is sent to catalytic reforming.

The product of the isomerization (or isomerate) is free of aromatic compounds in contrast to the refonnat which usually contains a significant amount due to dehydrocyclization reactions of paraffins and dehydrogenation of naphthenes.

Isomerate and reformate are usually sent to the gasoline pool in which other bases such as gasoline resulting from fluidized catalytic cracking (FCC) or additives such as methyl tertiary butyl ether (MTBE) can also be used.

Aromatics have high octane numbers favorable for their use in spark ignition engines, but for environmental reasons, their total content in gasoline is increasingly limited.

As of 2005, the European specification plans to reduce the total content of aromatics in super-fuels to a maximum of 35% by volume, whereas currently the content is of the order of 42% by volume.

It is therefore imperative to develop new processes for synthesizing gasoline bases that are free of aromatics but have high octane numbers.

The present invention relates more particularly to the isomerization of the C ₇ -rich fraction derived from atmospheric distillation naphtha.

Table 1 below gives the research octane number (RON) and the boiling points of the main hydrocarbon compounds present in the C7 cut obtained from atmospheric distillation naphtha: <u> Table 1 </ u> RON Teb (° C) trimethyl 2-2-3 butane 112.1 80.8 dimethyl 2-2 pentane 92.8 79.2 dimethyl 2-4 pentane 83.1 80.5 dimethyl 3-3 pentane 80.8 86 dimethyl 2-3 pentane 91.1 89.7 2-methyl hexane 42.4 90 3-methyl hexane 52 91.9 ethyl-3 pentane 65 93.4 n-heptane 0 98.4 1,1-dimethylcyclopentane 92.3 87.8 cis-dimethyl-1,3 cyclopentane 79.2 90.8 1,3-trans-1,3-dimethylcyclopentane 80.6 91.7 1,2-trans-1,2-dimethylcyclopentane 80.6 91.8 methyl-cyclohexane 74.8 100.9 ethyl-cyclopentane 67.2 103.4 toluene 120 110.7

The consideration of the octane numbers of the various C ₇ isomers shows that the isomers of normal-heptane (nC ₇ ) having several branches, ie the di and tribranchs have a sufficiently high octane number (from 80 to 110 ) to be sent directly to the gasoline pool.

On the other hand, isomers with only one branch or mono-branched, have insufficient octane numbers (42 for 2-methylhexane, 52 for 3-methylhexane) to be mixed with the gasoline pool.

These compounds must therefore be as much as possible converted into paraffins di or tribranched in the isomerization process.

As regards normal-heptane, its octane number being zero, it must imperatively be converted to extinction in the isomerization process.

Up to 1 wt.% Of nC7 in the isomerate and, if possible, less than 0.5 wt.% Can be tolerated.

Moreover, the toluene present in the fresh feedstock can be totally hydrogenated to methylcyclohexane (MCH), either in a specific hydrogenation unit, or in the paraffin isomerization unit which has a hydrogenating function.

This latter possibility is however not desirable because toluene has an excellent RON unlike that of MCH, and it may therefore be interesting to isolate it either for use as a solvent or as a petrochemical base, or with a view to reintroducing it into the gasoline pool as an octane enhancer at a level permitted by the specifications.

The methyl-cyclohexane (MCH) present in the feedstock in a relatively large amount, is very little affected by the isomerization, the isomerization catalysts not promoting the opening of naphthenic rings in their usual conditions of implementation.

However, the C ₇ feed may contain up to 30% by weight of methyl cyclohexane, a compound whose RON is less than 75, which significantly increases the RON of the C ₇ isomerate obtained.

It may therefore be advantageous to use a ring-opening unit that will essentially convert the MCH into normal and branched paraffins and send these paraffins to the isomerization unit.

It may also be advantageous to convert the naphthenes to aromatics in a specific dehydrogenation unit and then extract the aromatics obtained so as to send to the isomerization only paraffins.

The two possibilities mentioned above are obviously exclusive of each other since there would be no sense in using a reactor for opening naphthenic rings if these were previously converted into aromatics and then eliminated. last.

These various possibilities are part of the present invention and will be presented later as variants.

The problem that the present invention seeks to solve is that of the production of gasoline bases from a C ₇ fraction which have a search octane number (RON) of at least 80, with a content limited aromatic compounds, which makes it possible to anticipate the new regulations on the specifications of the gasoline pool.

• une première coupe contenant majoritairement des paraffines et des naphtènes qui est envoyée dans une unité d'isomérisation, et
• une deuxième coupe contenant majoritairement des composés aromatiques et notamment du toluène, qui pourra selon les besoins, être valorisée comme solvant, comme base pour la pétrochimie, ou être réintroduite au moins en partie dans le pool essence, tout en respectant la spécification sur la teneur finale en aromatiques.

The solution proposed in the present invention consists of a process for treating a C7 cut, generally resulting from an atmospheric distillation, so as to obtain two cuts:

• a first cut containing predominantly paraffins and naphthenes which is sent to an isomerization unit, and
• a second cut containing mainly aromatic compounds and especially toluene, which may be used as a solvent, as a base for petrochemistry, or be reintroduced at least partly in the gasoline pool, while respecting the specification on the content. final in aromatics.

The isomerization unit produces predominantly paraffinic effluents, and it is possible to treat them in a separation unit of normal and mono-branched paraffins on the one hand and di- and tri-branched paraffins on the other hand, so as to recycle until the normal paraffins and mono branched at the top of the isomerization unit are exhausted.

The amount of naphthenic that can be admitted into the feed at the inlet of the isomerization is limited only by the RON of the product isomerate.

In practice, the naphthenic content in the feedstock at the isomerization is around 20% by weight for most of the C7 feedstock from an atmospheric distillation naphtha.

In cases where the content of naphthenic compounds would be too high, it will always be possible to use the variant consisting of previously dehydrogenating naphthenes to aromatics or that taking into account the opening of naphthenic rings, as will be explained below.

One of the advantages of the invention is precisely by using the adapted variant, to be able to treat a C7 charge having any distribution in paraffins, naphthenes and aromatics. The invention thus makes it possible to obtain an isomerate containing a majority of branched di- and tri-branched paraffins whose RON can easily reach 80 or more.

By incorporating into this isomerate limited amounts of aromatic compounds, including toluene extracted upstream of the isomerization unit, it is possible to increase the RON to values of 85 or more.

Examination of the prior art:

The separation between aromatics and paraffins can be done either by extraction with solvent or by extractive distillation.

There are many patents using these techniques to extract benzene and / or toluene. We will mention as examples US Pat. No. 5,722,026; US 4, 168,209; U.S. 3,884,769.

In the case where the separation is carried out by solvent extraction, an implementation of the membrane contactor type can be used.

• Par adsorption sur des zéolithes ou du charbon actif, du gel de silice, de l'alumine ou des adsorbants polymèriques. Takahashi et al. dans AIChE Journal, 48(7), pp. 1457-1468, 2002 ont montré que des zéolithes de type faujasite adsorbent sélectivement les composés aromatiques.
• Par séparation sur membrane les matériaux membranaires utilisés pouvant être des matériaux minéraux ( par exemple de type zéolithiques) ou des polymères. Les brevets US 5, 643 442; US 5,635 055 et US 6, 187 987 proposent par exemple de séparer sélectivement les aromatiques grâce à une membrane en polyimide.

Other separation techniques are also possible:

• By adsorption on zeolites or activated charcoal, silica gel, alumina or polymeric adsorbents. Takahashi et al. in AIChE Journal, 48 (7), pp. 1457-1468, 2002 have shown that faujasite type zeolites selectively adsorb aromatic compounds.
• By membrane separation the membrane materials used may be inorganic materials (eg zeolites) or polymers. U.S. Patents 5,643,442; US Pat. No. 5,635,055 and US Pat. No. 6,187,987 propose, for example, to selectively separate aromatics by means of a polyimide membrane.

Yoshikawa and Tsubouchi have published a study in Separation Science and Technology, 35 (12), pp. 1863-1878, 2000 showing that filled copolymer membranes could also allow this separation.

Zeolite membranes of the faujasite structural type also have good selectivity with respect to aromatic molecules, as described in the articles by Nair et al. in Microporous and Mesoporous Materials, 48, pp 219-228, 2001 and Jeong et al. in Separation Science and Technology, 37 (6), pp 1225-1239, 2002.

Liquid membranes can also be used as described by A. L. GOSWAMI and B. RAWAT in Journal of Membrane Science No. 24, 145 of 1985.

There are relatively few patents concerning the valorization of the C7 cut by isomerization, most of them concerning the isomerization treatment of C5-C6 cuts. In addition, none of these processes allows the simultaneous production of an aromatic cut.

US Pat. No. 6,069,289 discloses a multi-branched paraffin separation process, optionally coupled to isomerization, but the treated feedstock does not contain naphthenic and aromatic compounds.

US Pat. No. 6,338,791 discloses a separation process coupled to an isomerization reactor. The separation process makes it possible to produce a cut rich in multibranched paraffins and optionally saturated or unsaturated cyclic compounds. This method makes it possible to produce a single slice because the naphthenes and aromatics of the filler are not separated from the paraffins, and are introduced in admixture with the paraffins in the isomerization reactor.

Brief description of the figures:

• FIG. 1 represents a process diagram according to the invention that does not contain a distillation column.
• FIG. 2 represents a process diagram according to the invention using a distillation column.
• FIG. 3 represents a process diagram according to the invention in its preferred variant using a distillation column and optionally comprising, on the head stream, a separation unit of linear and mono branched paraffins on the one hand, and di- and tri-branched paraffins, on the other hand, and on the bottom flow, an opening unit of the naphthenic rings.

Brief presentation of the invention :

The present invention must be placed in the more general context of the treatment of the naphtha fraction resulting from the atmospheric distillation of the crude.

1. 1) une fraction de tête comportant essentiellement les composés à 5 et 6 atomes de carbone qui est envoyée dans une isomérisation spécifique dont les conditions opératoires et le catalyseur peuvent être différents de ceux utilisés pour l'isomérisation de la coupe C₇.
2. 2) une fraction à 7 atomes de carbone qui fait l'objet du traitement décrit dans la présente invention et qui aboutit à un effluent à 7 atomes de carbone contenant au moins 70 % poids de paraffines di et tribranchées, et dont le nombre d'octane est compris entre 80 et 87.
3. 3) une fraction de fond contenant essentiellement les composés à 8 atomes de carbone et plus qui est envoyée dans une unité de reformage catalytique.

La présente invention porte sur le traitement de la fraction à 7 atomes de carbone issue du fractionnement précédent, mais étant donné les performances de la colonne de fractionnement du naphta, on pourra trouver dans la dite coupe C₇ jusqu'à 10 % de composés plus légers à 6 atomes de carbone ou moins, et jusqu'à 10 % de composés plus lourds à 8 atomes de carbone et plus.
La présente invention tient compte de ces composés adjacents à la coupe C7 proprement dite que l'on continuera à appeler par simplification "coupe C7".
La présente invention concerne donc un procédé de production de paraffines multi-branchées à 7 atomes de carbone à partir d'une charge comprenant en majeure partie des hydrocarbures à 7 atomes de carbone, permettant d'obtenir:

• Un isomérat ayant un indice d'octane au moins égal à 80 avec une teneur en composés aromatiques inférieure à 1 % poids, et préférentiellement inférieure à 0,5 % poids.
• Une coupe aromatique majoritairement constituée de toluène qui peut être utilisée comme solvant ou base pétrochimique ou être réintroduite dans le pool essence dans des proportions compatibles avec la spécification sur la teneur en aromatiques.

The naphtha section is generally separated into 3 fractions in a distillation column:

1. 1) a head fraction comprising essentially the compounds with 5 and 6 carbon atoms which is sent in a specific isomerization whose operating conditions and the catalyst may be different from those used for the isomerization of the C ₇ cut.
2. 2) a fraction with 7 carbon atoms which is the subject of the treatment described in the present invention and which results in an effluent with 7 carbon atoms containing at least 70% by weight of di- and tribranched paraffins, and whose number of octane is between 80 and 87.
3. 3) a bottom fraction essentially containing the compounds with 8 or more carbon atoms which is sent to a catalytic reforming unit.

The present invention relates to the treatment of the fraction with 7 carbon atoms resulting from the preceding fractionation, but given the performance of the naphtha fractionation column, it will be possible to find in said C ₇ fraction up to 10% of compounds more light to 6 carbon atoms or less, and up to 10% heavier compounds to 8 carbon atoms and more.
The present invention takes into account those compounds adjacent to the C7 section itself, which will continue to be called "C7 cut" simplification.
The present invention therefore relates to a process for producing multi-branched paraffins containing 7 carbon atoms from a feedstock comprising in the majority of hydrocarbons with 7 carbon atoms, making it possible to obtain:

• An isomer having an octane number of at least 80 with an aromatic content of less than 1% by weight, and preferably less than 0.5% by weight.
• An aromatic cut predominantly consisting of toluene that can be used as a solvent or petrochemical base or be reintroduced into the gasoline pool in proportions compatible with the specification on the aromatic content.

• normal-heptane de 20 à 40 % poids
• méthyl-2 hexane de 5 à 15 % poids
• méthyl-3 hexane de 10 à 20 % poids
• méthyl- cyclohexane de 5 à 30 % poids
• toluène de 4 à 15 % poids.

Generally, the C7 cut will have a composition in the following ranges for the main compounds:

• normal-heptane 20 to 40% by weight
• 2-methyl hexane 5 to 15% by weight
• 3-methyl hexane 10 to 20% by weight
• methylcyclohexane 5 to 30% by weight
• toluene from 4 to 15% by weight.

The whole of the paraffins therefore represents 55 to 90% by weight of the cut, methylcyclohexane of 5 to 30% by weight and toluene of 4 to 15% by weight.

1. 1) L'extraction des aromatiques de la charge C7 qui va laisser une coupe C7 ne contenant plus que des paraffines et des naphtènes.
2. 2) La transformation des normales paraffines en paraffines branchées, et des paraffines mono branchées en paraffines multibranchées ( di et tri branchées) qui est réalisée dans une unité d'isomérisation travaillant sous pression partielle d'hydrogène.
3. 3) la séparation des paraffines normales et mono branchées d'une part et des paraffines di et tri branchées d'autre part, pourra être réalisée par distillation ou par un procédé de séparation par adsorption par exemple dans une unité de type PSA ( Pressure Swing Adsorption qu'on peut traduire par unité d 'adsorption par variation de pression) ou de type contre courant simulé (CCS) de manière à recycler vers l'unité d' isomérisation les paraffines normales et mono branchées.
4. 4) De façon optionnelle, la déshydrogénation sélective des naphtènes en aromatiques qui se fera en amont de l'extraction des aromatiques.
5. 5) De façon optionnelle et en alternative à l'option 4, une unité d'ouverture de cycles naphtèniques qui permet de convertir ces derniers en paraffines linéaires ou monobranchées qui seront envoyées à l'unité d'isomérisation.

L'invention s'applique à une coupe C7 issue d'un naphta de distillation atmosphérique, mais plus généralement elle s'applique à une coupe C7 ayant des proportions quelconques en paraffines, naphtènes et aromatiques.
On entend par proportions quelconques, tout jeu de proportion dans lequel les familles paraffines, naphtènes et aromatiques sont présentes sans limitation de leur teneur.The transformation of the starting C7 cut into the final C7 cut composed of a majority of branched di- and tri-paraffins will be obtained by the following sequence of steps:

1. 1) The extraction of aromatics from the charge C7 which will leave a C7 cut containing only paraffins and naphthenes.
2. 2) The conversion of normal paraffins into branched paraffins, and mono branched paraffins into multibranched paraffins (di and tri branched) which is carried out in an isomerization unit working under partial pressure of hydrogen.
3. 3) the separation of normal and mono-branched paraffins on the one hand and di- and tri-branched paraffins on the other hand can be carried out by distillation or by an adsorption separation process for example in a PSA-type unit (Pressure Swing Adsorption that can be expressed per unit of adsorption by pressure variation) or counter-current type (CCS) to recycle normal and mono branched paraffins to the isomerization unit.
4. 4) Optionally, the selective dehydrogenation of naphthenes to aromatics which will be upstream of the extraction of aromatics.
5. 5) Optionally and as an alternative to Option 4, a naphthenic ring opening unit that converts the latter into linear or mono-branched paraffins which will be sent to the isomerization unit.

The invention applies to a C7 cut from an atmospheric distillation naphtha, but more generally it applies to a C7 cut having any proportions of paraffins, naphthenes and aromatics.
By any proportion is meant any proportional set in which the paraffin, naphthene and aromatic families are present without limitation of their content.

The present invention is therefore defined as a process for producing an RON isomerate at least equal to 80, and for coproduction of an aromatic cut consisting predominantly of toluene, from a 7-atom hydrocarbon fraction. carbon containing paraffins, naphthenes and aromatics in any proportion, said process using at least one aromatic extraction unit contained in the feed, at least one isomerization unit, and at least one separation unit of the linear and mono-branched paraffins on the one hand, and di- and tri-branched paraffins on the other hand, characterized in that the isomerate produced contains less than 1% by weight of aromatics and preferably less than 0.5% by weight of aromatics.

According to a first variant of the invention, the fresh feedstock (1) is introduced into an aromatics extraction unit (EA) which makes it possible firstly to produce an aromatic cut predominantly containing toluene (3), and secondly, a deflavored C7 cut (2) which is sent as feedstock from an isomerization unit (IS) whose effluent is after stabilization (5), introduced into a separation unit (SP) from which on the one hand linear and mono-branched paraffins (8) which are recycled to the input of the isomerization unit (IS) mixed with the effluent (2) from the aromatics extraction unit (EA), and on the other hand, a stream (9) rich in di- and tri-branched paraffins which constitutes the isomerate produced.

• a) un flux de tête (13) qui constitue l'isomérat produit
• b) un flux de fond (15) qui alimente l'unité d'isomérisation (IS)

l'effluent (18) de l'unité d'isomérisation, après stabilisation, étant recyclé vers la colonne de distillation (CD) à un niveau situé au dessus du niveau d'alimentation de la colonne.According to a second variant of the invention, the fresh charge (11). is introduced into an aromatics extraction unit (EA) which produces on the one hand an aromatic cut (23) containing predominantly toluene, and on the other hand a deflavored C7 cut (12) which is introduced into a column distiller (CD) from which we extract:

• a) a head flow (13) which constitutes the isomerate produced
• b) a bottom stream (15) which feeds the isomerization unit (IS)

the effluent (18) of the isomerization unit, after stabilization, being recycled to the distillation column (CD) at a level above the feed level of the column.

• a) un flux de tête (13) qui constitue l'isomérat produit
• b) un flux latéral (14) qui alimente l'unité d'isomérisation ( IS)
• c) un flux de fond (15) qui alimente l'unité d'isomérisation (IS) en mélange ave le flux latéral ( 14)

l'effluent (18) de l'unité d'isomérisation, après stabilisation, étant recyclé vers la colonne de distillation (CD) à un niveau situé au dessus du niveau de sortie du flux latéral (14).According to a variant of the previous one, the fresh charge (11). is introduced into an aromatics extraction unit (EA) which produces on the one hand an aromatic cut (23) containing predominantly toluene, and on the other hand a deflavored C7 cut (12) which is introduced into a column distiller (CD) from which we extract:

• a) a head flow (13) which constitutes the isomerate produced
• b) a side stream (14) which feeds the isomerization unit (IS)
• c) a bottom stream (15) which feeds the isomerization unit (IS) in admixture with the side stream (14)

the effluent (18) of the isomerization unit, after stabilization, being recycled to the distillation column (CD) at a level above the outlet level of the side stream (14).

According to a variant that can be applied when the process according to the invention comprises a distillation column, the top stream (13) of the distillation column (CD) is sent to a separation unit (SP) of the normal and mono branched paraffins. on the one hand, and di- and tri-branched paraffins on the other hand, the normal and mono-branched paraffins (21) being reintroduced into the isomerization unit (IS), and the branched di- and tri-paraffins (20) constituting the isomerate.

According to a third variant of the invention, the bottom stream (15) of the distillation column (CD) is sent to an opening unit of the naphthenic rings (OC) from which an effluent (16) is extracted which is sent at the isomerization unit (IS).

According to a variant which constitutes a sub-variant of the preceding one, the bottom stream (15) of the distillation column (CD) is sent to an opening unit of the naphthenic rings (OC) from which an effluent is extracted (16). which is sent to the feed of the column (CD) mixed with the flow (12).

The distillation column (CD) may advantageously be of the column type with an inner wall.

The separation unit of linear and mono-branched paraffins on the one hand, and branched di- and tri-branched paraffins, on the other hand, can be carried out by a PSA-type adsorption process.

In other cases, the separation of linear and mono-branched paraffins on the one hand, and di- and tri-branched paraffins on the other hand, may be carried out by a simulated counter-current type (CCS) adsorption method.

The extraction of aromatics (EA) may be carried out using a solvent.

In other cases, the aromatics extraction unit (EA) may be carried out by extractive distillation.

In still other cases, the aromatics extraction unit (EA) may be carried out by adsorption or by use of a membrane.

In all the variants which do not make use of an opening unit of the naphthenic rings, the C7 feedstock may be introduced into a naphthene-specific dehydrogenation unit upstream of the aromatics extraction unit.
Finally, in certain cases, it may be advantageous to place the aromatics extraction unit so that said unit is fed by the bottom flow of the column (CD), the deflavored effluent of said unit being sent to the isomerization unit (IS). This last variant is shown schematically in dotted lines in FIG.

• a) un flux de tête (13) qui constitue l'isomérat produit
• b) un flux de fond ( 15) qui alimente une unité d'extraction des aromatiques (EA) permettant de produire d'une part une coupe (25) contenant majoritairement des aromatiques, et d'autre part un effluent (26) qui est introduit dans l'unité d'isomérisation (IS),
  l'effluent (18) de l'unité d'isomérisation après stabilisation étant recyclé vers la colonne de distillation ( CD) à un niveau situé au dessus du niveau d'alimentation de la colonne.

According to this last variant, the process diagram is described as follows:
The fresh batch is introduced into a distillation column (CD) from which:

• a) a head flow (13) which constitutes the isomerate produced
• b) a bottom stream (15) which feeds an aromatics extraction unit (EA) for producing on the one hand a cut (25) containing predominantly aromatics, and on the other hand an effluent (26) which is introduced into the isomerization unit (IS),
  the effluent (18) of the isomerization unit after stabilization is recycled to the distillation column (CD) at a level above the feed level of the column.

• a) un flux de tête qui constitue l'isomérat produit
• b) un flux latéral ( 14) qui alimente l'unité d'isomérisation ( IS)
• c) un flux de fond ( 15) qui alimente une unité d'extraction des aromatiques ( EA) permettant de produire d'une part une coupe ( 25) contenant majoritairement des aromatiques, et d'autre part un effluent ( 26) qui est introduit en mélange avec le flux ( 14) dans l'unité d'isomérisation ( IS),

l'effluent ( 18) de l'unité d'isomérisation après stabilisation étant recyclé vers la colonne de distillation ( CD) à un niveau situé au dessus du niveau de sortie du flux latéral ( 14).In the case where a lateral flow of the column is furthermore extracted, the fresh feedstock is introduced into a distillation column (CD) from which:

• a) a head flow which constitutes the isomerate produced
• b) a side stream (14) which feeds the isomerization unit (IS)
• c) a bottom stream (15) which feeds an aromatics extraction unit (EA) for producing on the one hand a cut (25) containing predominantly aromatics, and on the other hand an effluent (26) which is introduced in admixture with the stream (14) in the isomerization unit (IS),

the effluent (18) of the isomerization unit after stabilization is recycled to the distillation column (CD) at a level above the outlet level of the side stream (14).

Detailed description of the invention

The detailed description of the invention will be better understood by following the process diagram of FIG. 1 for the first part of the description, then of FIGS. 2 and 3 for the second part of the description.

• normal-heptane de 20 à 40 % poids,
• méthyl-2 hexane de 5 à 15 % poids,
• méthyl-3 hexane de 10 à 20% poids,
• méthyl-cyclohexane de 5 à 30 % poids,
• toluène de 4 à 15 % poids.

The filler used to illustrate the invention is a C7 cut from an atmospheric distillation naphtha. It has the chemical composition given below:

• normal-heptane of 20 to 40% by weight,
• 2-methylhexane of 5 to 15% by weight,
• 3-methylhexane of 10 to 20% by weight,
• methylcyclohexane of 5 to 30% by weight,
• toluene from 4 to 15% by weight.

In the scheme described in FIG. 1, the fresh feedstock (1) is introduced into an aromatics extraction unit (EA) from which a flow (3) containing a majority of of aromatic compounds and especially toluene and a stream (2) containing a majority of paraffinic and naphthenic compounds which is sent to the isomerization unit (IS).
The effluent (5) of the isomerization unit is sent to a stabilization column (ST) which makes it possible to release a stream (6) consisting of light gases at the top
The effluent (7) of the stabilization column (ST) containing branched di- and tri-branched paraffins, naphthenic rings, but also linear and mono-branched paraffins is sent to a separation unit (SP) of the linear and mono-branched paraffins. on the one hand and paraffins di and tri branched on the other.
The effluent (9) of the separation unit (SP) composed of a majority of di- and tri-branched paraffins is the isomerate, while the effluent (8) of the separation unit (SP) consists of a majority of linear and mono branched paraffins is returned to the isomerization unit in admixture with the stream (2).
The flow (4) consists of hydrogen for the needs of the isomerization unit which works under partial pressure of hydrogen.

The aromatics extraction unit (EA) may use any technique known to those skilled in the art. It is possible, for example, to employ either a solvent extraction technique such as DMSO or sulfolane, or an extractive distillation technique using a solvent such as N-methylpyrrolidone, or dimethylformamide or tetraethylene glycol.
With these processes, it is possible to extract a cut having an aromatic content of at least 99.0 wt%.

The isomerization unit (IS) transforms normal and mono branched paraffins into multi-branched paraffins. The isomerization catalyst used in said unit will be included in the group consisting of supported catalysts containing at least one halogen and at least one Group VIII metal, zeolitic catalysts containing at least one Group VIIII metal, Friedel catalysts and Krafts, super acid catalysts of type HPA on zirconia, WOx on zirconia, or sulphated zirconia.
The total pressure in the isomerization reaction zone is from about 10 to 50 10 ⁵ Pascals relative, the hourly space velocity being from about 0.2 to 10 hours ^-1.
The hydrogen / hydrocarbon molar ratio is between 0.06 and 30 mol / mol and
preferably between 0.1 and 0.5 mol / mol.
The temperature in the reaction zone is between 50 and 150 ° C, and preferably between 60 and 100 ° C.

The separation unit (SP) of the linear and mono-branched paraffins on the one hand and the di- and tri-branched paraffins on the other hand may use any technique known to those skilled in the art.
Among these, there may be mentioned the pressure swing adsorption process known by the abbreviation PSA or the simulated countercurrent separation (CCS) method.
In the case where the separation (SP) is carried out by an adsorption unit, any adsorbent or adsorbent mixture having a selectivity in favor of linear and mono-branched paraffins may be used, in particular the MFI, FER type zeolite adsorbents. , FAU, BEA, EUO, MTT, MEL, IRON, AFI, ATO, AEL, NES and MWW, LTA, or any adsorbent as described in US Pat. No. 6,353,144, FR 02/09841 and patent application US20020045793.

The adsorptive separation (SP) can be carried out in the gas phase by a PSA or CCS type process. In this case, the operating temperature of the unit is between 150 and 400 ° C. In the case of an implementation in PSA, the pressure of the column during the adsorption phase is between 2 and 30 ⁵ Pascals, and during the desorption phase between 0.5 and 5 10 ⁵ Pa.
The desorbent used may be an inert gas, such as hydrogen or nitrogen, or a hydrocarbon, such as C3-C6 paraffins.
Hydrogen is also a desorbent particularly well suited for this separation, since it can be directly recycled to the isomerization reactor with the desorbate (effluent from the desorption unit rich in normal and branched paraffins).
Such a separation unit (SP) in the gas phase makes it possible to produce an isomer of RON at least equal to 80.

Alternatively, the adsorption separation (SP) can be carried out in the liquid phase by a CCS type process. In this case, the operating temperature of the unit is between 100 and 250 ° C. The pressure in the unit is between 2 and 20 10 ⁵ Pa.
The desorbent used is preferably a hydrocarbon, and may be in particular C3-C6 paraffins.
Such a separation unit by CCS in the liquid phase also makes it possible to produce an isomer of RON at least equal to 80.

In the variant illustrated in FIG. 2, the fresh feedstock (11) is introduced into the aromatics extraction unit (EA), from which a stream (23) rich in aromatics and containing predominantly toluene, and a stream ( 12) rich in paraffinic compounds and
naphthenic which is sent in a distillation column (CD).
The aromatics extraction unit may use any technique known to those skilled in the art, such as those proposed in the description of FIG.
The values given below are typical values which in no way limit the invention. The distillation column (CD) has about 100 trays and the supply is made in the vicinity of the tray 50 (numbered with respect to the column head). ).
The temperature at the top of the column is close to 95 ° C. for a pressure of 1.5 × 10 ⁵ Pascals; the temperature at the column bottom was 127 ° C at a pressure 2 10 ⁵ Pascals is the column head extracts (CD) a stream (13) rich in di and tri-branched paraffins constitutes the isomerate.
A bottom stream (15) is withdrawn from the column (CD) which optionally can supply the aromatics extraction unit (EA) when the latter is not directly fed by the fresh feed (11).
The effluents from the aromatics extraction unit are then sent to the isomerization unit (IS), optionally mixed with a side stream (14).
When the aromatics extraction unit is fed with the fresh feed (11), the bottom stream (15) is sent directly to the isomerization unit (IS).
Optionally, a side stream (14) containing paraffinic and naphthenic compounds which is mixed with the bottom stream (15) in the isomerization unit (IS) can be withdrawn laterally at the plateau 44. The latter is operated under the same conditions as those provided in the description of FIG.
The effluent (17) of the isomerization unit containing a stream enriched in branched mono, di and tri paraffins is sent to the stabilization column (ST) from which a gas-rich fraction (19) is discharged at the top and a stabilized effluent (18), ie free of overhead gases, which is recycled to the distillation column (CD) at a level above the extraction level of the lateral flow (14).
This stream (18) containing linear paraffins, mono di and tri branched will benefit from the separation effect of the column (CD) insofar as branched di paraffins and branched with a boiling point generally lower than that of linear or mono branched paraffins, will be found preferentially at the head of the column (CD) to constitute the flow of head (13).

In a preferred variant of the invention represented by FIG. 3, the diagram of FIG. 2 is repeated, to which is added on the bottom flow (15) of the column (CD) a unit for opening naphthenic rings (OC). which will produce a paraffin-enriched stream (16) which is mixed with the side stream (14) to the isomerization unit (IS).
This flow (16) may in another variant be returned to the supply of the column (CD) in mixture with the flow (12).
The opening unit of the naphthenic rings (OC) makes it possible to transform naphthenes into linear and branched paraffins. The catalyst used in said unit may be any catalyst for converting by ring opening at least 5% by weight of methylcyclohexane present in the mixture to be treated.
The pressure in the ring opening reaction zone is about 5 to 50 bar (1 bar = 10 ⁵ Pascals, the hourly space velocity is about 0.5 to 20 h -1). the hydrocarbon is between 0.5 and 10 moles / mole The temperature in the reaction zone is between 200 and 400 ° C, and preferably between 250 and 350 ° C.
It is also possible to add to the diagram illustrated in FIG. 3 a separation unit of the linear and mono-branched paraffins on the one hand and di- and tri-branched paraffins connected on the other hand fed by the head stream (13) and which produces an effluent (20) enriched in branched di- and tri-branched paraffins which constitutes the isomerate and a stream (21) enriched in linear and mono-branched paraffins which is returned to the hydroisomerisation unit (IS) in admixture with the side stream (14) and the effluent from the ring opening reactor (16).

• pression: 3 à 15 bars relatifs
• température moyenne: 350 à 400°C
• PPH: 1 à 10 h-1
• ratio hydrogène/hydrocarbure = 2 à 6 moles/mole

The separation unit of the linear and mono-branched paraffins on the one hand and di- and tri-branched paraffins on the other hand has the same characteristics and operates in the same conditions as those described in the diagram of FIG.
Finally, as an alternative to each of the diagrams corresponding to FIGS. 1 or 2, a naphthene-specific dehydrogenation unit may be placed upstream of the aromatics extraction unit.
This unit, employing a catalyst of the group consisting of supported catalysts containing at least one Group VIII metal, operates under the following conditions:

• pressure: 3 to 15 bar relative
• average temperature: 350 to 400 ° C
• PPH: 1 to 10 h-1
• hydrogen / hydrocarbon ratio = 2 to 6 moles / mole

Example 1

Example 1 illustrates the preferred variant in accordance with FIG. 3, and uses in addition aromatic aromatics (EA) and isomerization (IS) base units, a naphthenic ring opening unit (OC) fed by the feed stream. bottom of the distillation column.
The feed to be treated (11) is introduced into an aromatics extraction unit (EA) which carries out an extractive distillation with N-methylpyrrolidone.

The fresh batch (11) has in the example considered the following composition (in% by weight) and a mass flow rate given below: dimethyl 2-3 butane 0.01 2-methyl pentane 0.13 methyl-3 pentane 0.17 n-hexane 1.41 methyl-cyclopentane 0.60 cyclohexane 1.73 benzene 0.33 trimethyl 2-2-3 butane 0.08 dimethyl 2-2 pentane 0.20 dimethyl 2-3 pentane 3.56 dimethyl 2-4 pentane 0.49 dimethyl 3-3 pentane 0.25 2-methyl hexane 8.99 3-methyl hexane 12.24 ethyl-3 pentane 1.14 n-heptane 31,45 1,1-dimethylcyclopentane 0.82 cis-dimethyl-1,3 cyclopentane 2.29 1,3-trans-1,3-dimethylcyclopentane 2.21 1,2-trans-1,2-dimethylcyclopentane 4.19 methyl-cyclohexane 12.97 ethyl-cyclopentane 0.73 toluene 13.51 C ₈ + 0.50 total flow (kg / hour) 11078

The rich aromatic section (23) has in the example considered the following composition (in% by weight) and a mass flow rate given below: benzene 2.37 toluene 97.03 Other compounds 0.60 total flow (kg / hour) 1527

With extractive distillation with N-methylpyrrolidone, it is possible, as in this example, to recover 99% of the aromatics and to obtain a cut with a purity greater than 99%.

The flow (12) rich in paraffinic and naphthenic compounds from the aromatics extraction unit is fed into a distillation column (CD) comprising 88 actual trays at the tray 50. The weight composition and the flow rate the mass of this flux (12) are as follows: dimethyl 2-3 butane 0.02 2-methyl pentane 0.14 methyl-3 pentane 0.18 n-hexane 1.63 methyl-cyclopentane 0.70 cyclohexane 2.01 benzene 0.00 trimethyl 2-2-3 butane 0.09 dimethyl 2-2 pentane 0.24 dimethyl 2-3 pentane 4.13 dimethyl 2-4 pentane 0.57 dimethyl 3-3 pentane 0.29 2-methyl hexane 10.42 3-methyl hexane 14.19 ethyl-3 pentane 1.31 n-heptane 36.42 1,1-dimethylcyclopentane 0.95 cis-dimethyl-1,3 cyclopentane 2.66 1,3-trans-1,3-dimethylcyclopentane 2.57 1,2-trans-1,2-dimethylcyclopentane 4.86 methyl-cyclohexane 15,03 ethyl-cyclopentane 0.85 toluene 0.16 C ₈ + 0.58 total flow (kg / hour) 9551

At the top of the column (CD), a stream (13) is produced which corresponds to the isomerate produced when an additional unit for separating the normal and monobranched paraffins is not added on the one hand and the paraffins on the other hand.
the weight composition and the mass flow rate of this stream 13 are as follows: isopentane 3.15 dimethyl 2-2 butane 0.20 dimethyl 2-3 butane 0.17 2-methyl pentane 0.81 methyl-3 pentane 0.53 n-hexane 2.19 methyl-cyclopentane 1.13 cyclohexane 2.07 benzene 0.00 trimethyl 2-2-3 butane 7.15 dimethyl 2-2 pentane 21.94 dimethyl 2-3 pentane 1.19 dimethyl 2-4 pentane 45.79 dimethyl 3-3 pentane 3.64 2-methyl hexane 6.14 3-methyl hexane 2.58 ethyl-3 pentane 0.08 n-heptane 0.50 1,1-dimethylcyclopentane 0.24 cis-dimethyl-1,3 cyclopentane 0.10 1,3-trans-1,3-dimethylcyclopentane 0.08 1,2-trans-1,2-dimethylcyclopentane 0.07 methyl-cyclohexane 0.25 ethyl-cyclopentane 0.00 toluene 0.00 C ₈ + 0.00 total flow (kg / hour) 7893

The RON of this isomerate (stream 13) is 82.8 and its aromatic content is less than 0.01 wt%.

At the tray 44 is drawn a stream (14) containing a majority (at least 60%) of normal-heptane and paraffins C ₇ mono-branched.
At the bottom of the column (CD) is drawn a stream (15) rich in methylcyclohexane and n-heptane.
This stream (15) is sent to a ring opening unit (OC) which produces an effluent (16) mainly containing a mixture of paraffins resulting in part from the opening of the rings, as well as unconverted methylcyclohexane.
In this example, the ring opening unit uses an iridium catalyst deposited on alumina or silica-alumina, such as that described in the application WO 02/07881.

• Température = 300 °C
• Pression = 14 bars.eff
• PPH = 10 heure^-1
• Ratio molaire hydrogène/hydrocarbure = 6 moles/mole

The opening unit of cycles is operated under the following conditions:

• Temperature = 300 ° C
• Pressure = 14 bars.eff
• PPH = 10 hours ^-1
• Hydrogen / hydrocarbon molar ratio = 6 moles / mole

The weight composition and the mass flow rate (excluding hydrogen) of the stream (16) corresponding to the effluent of the ring opening unit are as follows: C ₅ - 1.83 paraffins C ₅ 3.71 paraffins C ₆ 1.72 methyl-cyclopentane 0.00 cyclohexane 0.00 benzene 0.00 paraffins C ₇ 78.32 1,1-dimethylcyclopentane 0.39 cis-dimethyl-1,3 cyclopentane 0.37 1,3-trans-1,3-dimethylcyclopentane 0.40 1,2-trans-1,2-dimethylcyclopentane 0.40 methyl-cyclohexane 11.51 ethyl-cyclopentane 0.39 toluene 0.18 C ₈ + 0.78 total flow (kg / hour) 6891

The stream (16) is mixed with the stream (14) to give a stream (22) which is introduced into an isomerization unit (IS) using a platinum catalyst on chlorinated alumina as described in the application US20020002319 A1.

• Température = 90 °C
• Pression = 30 bars.eff
• PPH = 1 heure^-1
• Ratio molaire hydrogène/hydrocarbure = 0,2 mole/mole

The isomerization unit works under the following conditions:

• Temperature = 90 ° C
• Pressure = 30 bars.eff
• PPH = 1 hour ^-1
• Hydrogen / hydrocarbon molar ratio = 0.2 mol / mol

The weight composition and the mass flow rate (excluding hydrogen) of the stream (17) corresponding to the effluent of the isomerization unit are as follows: C ₅ - 2.48 isopentane 0.37 dimethyl 2-2 butane 0.02 dimethyl 2-3 butane 0.02 2-methyl pentane 0.08 methyl-3 pentane 0.04 n-hexane 0.10 methyl-cyclopentane 0.07 cyclohexane 0.18 benzene 0.00 trimethyl 2-2-3 butane 1.66 dimethyl 2-2 pentane 3.32 dimethyl 2-3 pentane 4.15 dimethyl 2-4 pentane 8.30 dimethyl 3-3 pentane 4.15 2-methyl hexane 22.40 3-methyl hexane 16.59 ethyl-3 pentane 0.83 n-heptane 21.57 1,1-dimethylcyclopentane 0.30 cis-dimethyl-1,3 cyclopentane 0.29 1,3-trans-1,3-dimethylcyclopentane 0.31 1,2-trans-1,2-dimethylcyclopentane 0.30 methyl-cyclohexane 12,17 ethyl-cyclopentane 0.30 toluene 0.00 C ₈₊ 0.00 total flow (kg / hour) 66802

The effluent (17) of the isomerization unit is sent to a stabilization column (ST) from which a flow (19) comprising the light gases resulting from the reactions of cracking within the isomerization unit (C _5- cut) and bottom a flow (18) whose composition is very close to that of the stream (17) and which is reintroduced at the top of the column (CD) at plateau level 12.
The mass flow (excluding hydrogen) of the flow (19) is 1658 kg / h.
It can be verified that the mass flow rate of the flow (11) is equal to the sum of the mass flow rates (excluding hydrogen) of the flows (23), (13), (19).

In conclusion, the example detailed above shows that it is possible to produce an isomer of RON greater than 80 (82.8) and containing less than 0.5% by weight (0.01%) of aromatics and co-product an aromatic cut rich in toluene (97% by weight) starting from a C7 load containing. 61% paraffins, 25% naphthenes and 14% aromatics.

Claims (16)

A process for producing an RON isomerate of at least 80, and co-producing an aromatic cut consisting predominantly of toluene, from a 7-carbon hydrocarbon fraction containing paraffins, naphthenes and in any proportion, said process using at least one aromatic extraction unit contained in the feedstock, at least one isomerization unit, and at least one linear and mono branched paraffin separation unit of a on the one hand, and di- and tri-branched paraffins on the other hand, characterized in that the isomerate produced contains less than 1% by weight of aromatics and preferably less than 0.5% by weight of aromatics. Process according to Claim 1, characterized in that the fresh feedstock (1) is introduced into an aromatics extraction unit (EA) which makes it possible to produce on the one hand an aromatic cut predominantly containing toluene (3) and on the other hand a deflavored C7 cut (2) which is sent as a feedstock from an isomerization unit (IS) whose effluent is after stabilization (5), introduced into a separation unit (SP) from which linear and mono-branched paraffins (8) which are recycled to the input of the isomerization unit (IS) in admixture with the effluent (2) from the aromatics extraction unit (EA), and on the other hand, a stream (9) rich in branched and branched paraffins which constitutes the isomerate produced. Process according to Claim 1, characterized in that the fresh filler (11). is introduced into an aromatics extraction unit (EA) which produces on the one hand an aromatic cut (23) containing predominantly toluene, and on the other hand a deflavored C7 cut (12) which is introduced into a column distiller (CD) from which we extract: a) a head flow (13) which constitutes the isomerate produced b) a bottom stream (15) which feeds the isomerization unit (IS)
the effluent (18) of the isomerization unit after stabilization is recycled to the distillation column (CD) at a level above the feed level of the column. Process according to Claim 1, characterized in that the fresh filler (11). is introduced into an aromatics extraction unit (EA) which produces on the one hand an aromatic cut (23) containing predominantly toluene, and on the other hand a deflavored C7 cut (12) which is introduced into a column distiller (CD) from which we extract: a) a head flow (13) which constitutes the isomerate produced b) a side stream (14) which feeds the isomerization unit (IS) c) a bottom stream (15) which feeds the isomerization unit (IS) in admixture with the side stream (14)
the effluent (18) of the isomerization unit after stabilization is recycled to the distillation column (CD) at a level above the outlet level of the side stream (14). Process according to claim 1, in which the fresh feed is introduced into a distillation column (CD) from which: a) a head flow (13) which constitutes the isomerate produced b) a bottom stream (15) which feeds an aromatics extraction unit (EA) for producing on the one hand a cut (25) containing predominantly aromatics, and on the other hand an effluent (26) which is introduced into the isomerization unit (IS),
the effluent (18) of the isomerization unit after stabilization is recycled to the distillation column (CD) at a level above the feed level of the column. Process according to Claim 1, in which the fresh feedstock is introduced into a distillation column (CD) from which: a) a head flow which constitutes the isomerate produced b) a side stream (14) which feeds the isomerization unit (IS) c) a bottom stream (15) which feeds an aromatics extraction unit (EA) for producing on the one hand a cut (25) containing predominantly aromatics, and on the other hand an effluent (26) which is introduced in admixture with the stream (14) in the isomerization unit (IS),
the effluent (18) of the isomerization unit after stabilization is recycled to the distillation column (CD) at a level above the outlet level of the side stream (14). Process according to any one of Claims 3 to 4, characterized in that the bottom stream (15) of the distillation column (CD) is sent to an opening unit of the naphthenic rings (OC) from which an effluent is extracted. (16) which is sent to the isomerization unit (IS). Process according to any one of Claims 3 to 4, characterized in that the bottom stream (15) of the distillation column (CD) is sent to an opening unit of the naphthenic rings (OC) from which an effluent is extracted. (16) which is fed to the column feed (CD) in admixture with the stream (12). Process according to any one of Claims 3 to 8, characterized in that the head stream (13) of the distillation column (CD) is sent to a separation unit (SP) of the normal and mono branched paraffins on the one hand. and branched and di-branched paraffins on the other hand, the normal and mono-branched paraffins (21) being reintroduced into the isomerization unit (IS), and the branched di- and tri-branched paraffins (20) constituting the isomerate. A process as claimed in any one of claims 3 to 9 wherein the distillation column (CD) is of the inner wall column type. Process according to any one of Claims 9 to 10, in which the separation of linear and mono-branched paraffins on the one hand, and branched di- and tri-paraffins, on the other, is carried out by a PSA adsorption process Process according to any one of Claims 9 to 10, in which the separation of linear and mono-branched paraffins on the one hand, and branched di- and tri-paraffins, on the other hand, is carried out by an adsorption process. Counter current simulated type (CCS). Process according to any one of claims 1 to 12 wherein the extraction of aromatics (EA) is carried out using a solvent. Process according to any one of claims 1 to 12 wherein the aromatics extraction unit (EA) is carried out by extractive distillation. Process according to any one of claims 1 to 12 wherein the aromatics extraction unit (EA) is carried out by adsorption or by use of a membrane. Process according to any one of claims 1 to 6 and 9 to 15 wherein the C7 feedstock is introduced into a naphthene-specific dehydrogenation unit upstream of the aromatics extraction unit.

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