EP0552072B1 - Lowering of the benzene contact of gasolines - Google Patents

Description

The invention relates to the reduction of the benzene content in fractions gasolines by a process associating the hydrogenation of the benzene contained in the light reformate and the isomerization of the effluent from the hydrogenation.

PRIOR ART

Environmental issues will jointly lead to the reduction of lead content and reduction of benzene content in gasoline fractions, preferably without reduction in octane number. This leads to the need for a rearrangement of the different hydrocarbons present in the essence fractions.

Catalytic reforming used under severe conditions and the isomerization of normal C ₅ -C ₆ paraffins with low octane numbers are the most commonly used processes currently used to obtain high octane numbers without the addition of lead. However, the catalytic reforming process produces significant amounts of high octane benzene. This is why it is necessary to develop new processes which make it possible to reduce the benzene content of gasolines while meeting the specifications for the octane number.

The combination of catalytic reforming and isomerization processes, consisting in separating the C ₅ -C ₆ fraction from the reformate, in isomerizing it and in introducing it directly into the gasoline fractions to improve the octane number is well known. ; it is described for example in patents US-A 4,457,832, US-A 4,181,599 and US-A 3,761,392. The reduction of the benzene content of the reformate can also be carried out in various ways, such as for example the modification of the naphtha cutting point between reforming and isomerization or the separation of the reformate into two fractions: a heavy reformate and a light reformate in which all the benzene is concentrated. This light fraction is then sent to a hydrogenation unit which makes it possible to transform the benzene into naphthenes, which are then decyclized in an isomerization unit working under severe conditions. The normal paraffins thus formed are isomerized by a conventional isomerization process (US-A 5,003,118). In the case of an isomerization catalyst based on chlorinated alumina, the naphthenes adsorb on the catalyst and thus contribute to deteriorating its activity.

US-A 3,611,117 also describes a process for hydro-isomerization cyclic hydrocarbons that uses a Group VIII metal supported on zeolite as a catalyst for opening cycles in severe operating conditions and as an isomerization catalyst in mild operating conditions.

One of the major problems of reducing the benzene content by saturation followed by decyclization and isomerization of the paraffins formed is the possible decrease in the octane number of the charge.

The object of the present invention is to reduce the benzene content in the gasolines without significant decrease in the octane number. The process of present invention therefore comprises the hydrogenation of benzene contained in the charge defined below in a hydrogenation zone and then the isomerization effluent from hydrogenation in an isomerization zone. In the method according to the parallel application, EP-A-0 552 070, a cut C5-C6 is mixed with said effluent.

DETAILED DESCRIPTION OF THE INVENTION

The hydrogenation zone and the isomerization zone according to the invention can be included in the same reactor, or in separate reactors such that each of said zones is included in at least one reactor.

In addition, the conditions under which the hydrogenation and isomerization, namely the operating conditions, the catalyst, etc. known to those skilled in the art. They are nevertheless specified below.

• paraffines : entre 40,0 et 80,0 %
• naphtènes : entre 0,5 et 7,0 %
• aromatiques : entre 6,0 et 45,0 %.

The feed concerned by the present invention generally consists of the light fraction obtained by distillation of a reformate. The maximum distillation temperature of this fraction is between 70 and 90 ° C, preferably between 77 and 83 ° C. The weight composition by families of hydrocarbons of this light fraction of the reformate is variable according to the following intervals:

• paraffins: between 40.0 and 80.0%
• naphthenes: between 0.5 and 7.0%
• aromatic: between 6.0 and 45.0%.

Benzene is essentially the only aromatic compound included in said fraction.

Furthermore, said fraction can comprise between 1 and 3% of hydrocarbons olefinic.

• le poids moléculaire moyen est compris entre 70 et 90 g/mol
• la masse volumique, mesurée à 15° C, est comprise entre 0,670 et 0,780 g/cm³
• la valeur de l'indice d'octane recherche est généralement comprise entre 75 et 90.

On the other hand, the light fraction of the reformate as described above has the following characteristics:

• the average molecular weight is between 70 and 90 g / mol
• the density, measured at 15 ° C, is between 0.670 and 0.780 g / cm ³
• the value of the research octane number is generally between 75 and 90.

The hydrocarbon feedstock concerned by the present invention is the fraction slight from a reformate or any other filler from another process or set of processes and having characteristics similar to those described above.

Said charge, the composition of which is described above, is sent to a hydrogenation zone, the operating characteristics of which are given below.

The pressure is between 1 and 60 bar (absolute), particularly from 2 to 50 bar and more advantageously from 5 to 45 bar.

The temperature is between 100 and 400 ° C, more advantageously between 150 (even 110) and 350 ° C and preferably between 160 (even 110) and 320 ° C.

The space velocity calculated relative to the catalyst is between 1 and 50 h ^-1 and more particularly between 1 and 30 h ^-1 (volume of charge per volume of catalyst and per hour).

The flow of hydrogen, relative to the catalyst, is between 1 and 2000 volumes (gas at normal conditions) by volume of catalyst and by hour.

The heat released at this stage is advantageously used to preheat the isomerization charge.

The catalyst used in the hydrogenation zone which is the subject of the present invention comprises at least one metal M chosen from the group formed by nickel, platinum and palladium, deposited on a support. Metal M must be in reduced form at less for 50% of its totality. Preferably nickel or platinum is used, and even more preferably platinum.

When using platinum or palladium the catalyst may contain advantageously at least one halogen in a proportion by weight per ratio to the catalyst of between 0.5 and 2%. Preferably, we uses chlorine or fluorine or a combination of both in a proportion relative to the total weight of catalyst between 0.5 and 1.5%.

In the case of the use of nickel, the proportion of metal M relative to the total weight of catalyst is between 0.1 and 60%, more particularly between 5 and 60% and preferably between 5 and 30%. In the case of the use of platinum and / or palladium, the total proportion of metal M by relative to the total weight of catalyst is between 0.1 and 10% and so preferred between 0.05 and 5%.

The support can be chosen from the group formed by alumina, silica-aluminas, silica, zeolites, activated carbon, clays and cements aluminous.

An alumina is preferably used, with a specific surface at least equal to 50 m ² / g and a pore volume at least equal to 0.4 cm ³ / g, for example with a specific surface of between 50 and 350 m ² / g and of pore volume between 0.4 and 1.2 cm ³ / g.

• teneur en paraffines comprise entre 40 et 80 %
• teneur en naphtènes comprise entre 19,5 et 59,5 %
• teneur en aromatiques inférieure à 0,1 %

The effluent from the catalytic hydrogenation zone has the following composition:

• paraffin content between 40 and 80%
• naphthenes content between 19.5 and 59.5%
• aromatic content less than 0.1%

The value of the research octane number (RON) of this effluent is included between 70 and 85.

Said effluent is sent with hydrogen to the isomerization zone and is brought into contact with an isomerization catalyst under the conditions of the isomerization specified below.

The catalyst used in the isomerization zone according to the process of the present invention is a catalyst comprising at least one group VIII metal and a zeolite. Different zeolites can be used for said catalyst, such as, for example, mordenite or Ω zeolite. Use is preferably made of a mordenite having an Si / Al (atomic) ratio of between 5 and 50 and preferably between 5 and 30, a sodium content of less than 0.2% and preferably of less than 0.1% ( relative to the weight of dry zeolite), a volume of mesh V of the elementary mesh of between 2.78 and 2.73 nm ³ and preferably between 2.77 and 2.74 nm ³ , an absorption capacity of benzene greater than 5% and preferably greater than 8% (relative to the weight of dry solid). The mordenite thus prepared is then mixed with a generally amorphous matrix (alumina, silica alumina, kaolin, etc.) and shaped by any method known to those skilled in the art (extrusion, pelletizing, coating). The mordenite content of the support thus obtained must be greater than 40% and preferably greater than 60% by weight.

At least one hydrogenating metal from group VIII, preferably chosen from the group formed by platinum, palladium, and nickel, is then deposited on this support, either in the form of a tetramine complex by cation exchange, either in the form of hexachloroplatinic acid in the case of platinum or in form of palladium chloride by anion exchange.

In the case of platinum or palladium, the content by weight is between 0.05 and 1% and preferably between 0.1 and 0.6%. In the case of nickel the weight content is between 0.1 and 10% and preferably between 0.2 and 5%.

The isomerization process is carried out between 230 and 280 ° C, at a partial pressure of hydrogen between atmospheric pressure and 70 bar and preferably between 5 and 50 bar. The space velocity is between 0.2 and 10 and preferably between 0.5 and 5 liters of liquid hydrocarbons per liter of catalyst and per hour. The hydrogen / charge molar ratio is normally between 0.5 and 10 and preferably between 1 and 3.

To near research octane number measurement errors which are equal to ± 0.5, the effluent thus obtained, in addition to its low benzene content, then has a research octane number practically equivalent to that of the reformate light before hydrogenation; it can thus be directly incorporated into the essence fractions. The method according to the invention therefore does not lead to a notable decrease in the research octane number and it makes it possible to decrease the benzene content.

The single figure shows an arrangement of the method according to the invention, in which the hydrogenation and isomerization reactions are carried out in two separate reactors (or units).

The stabilized reformate (1) is sent to a distillation column (6) which is comes out, in the background a heavy reformate (3) which can be used directly in the essence fractions and at the top a slight reformate (2). The latter is sent to a hydrogenation unit (7) then the cut obtained (4) is treated in a isomerization unit (8) giving the final product (5) which, after stabilization, can be used in essence fractions.

The example which follows defines the invention without limiting its scope.

Example 1

The light reformate obtained after distillation at 85 ° C., containing 21.5% of benzene, having an octane number of 80.3 and the detailed composition of which is given in Table I, is sent to a hydrogenation unit at a temperature of 110 ° C and a pressure of 40 bar. The hydrogen to hydrocarbons molar ratio contained in the charge is equal to 0.85, and the liquid space velocity equal to 4 h ^-1 . The catalyst used in the hydrogenation section consists of 15% of Ni deposited on alumina.

The effluent from the hydrogenation unit, the detailed composition of which appears in Table I, no longer contains benzene but has an octane number of 76.5. It is then sent to an isomerization unit operating at a temperature of 260 ° C., a pressure of 30 bars with an LHSV equal to 2 h ^-1 and a hydrogen to hydrocarbon molar ratio of the charge equal to 4. The catalyst used in the isomerization unit contains 0.3% platinum deposited on a support composed of 80% mordenite with Si / Al ratio = 11 and 20% alumina. The effluent leaving the isomerization unit has the composition given in Table I; it no longer contains benzene and has an octane number of 80, practically equivalent to the octane number of the light reformate. This effluent can be directly incorporated into the gasoline fractions after stabilization. Light reformate (% by weight) Hydrogenation effluent Isomerization outlet effluent light 6.5 6.5 7.45 iC5 9.9 9.9 10.55 nC5 7.1 7.1 7.0 22DMC4 3.0 3.0 6.65 23DMC4 4.1 4.1 5.35 2MC5 15.8 15.8 19.55 3MC5 12.5 12.5 12.9 nC6 12.1 12.1 9.75 C7 3.5 3.5 1.6 CC5 0.4 0.4 0.45 MCC5 3.6 3.6 14.45 Benzene 21.5 - - CC6 0 21.5 4.3 RON 80.3 76.5 80 • iC ₅ corresponds to isoparaffin C ₅ • nC ₅ corresponds to normal paraffin C ₅ • 22DMC ₄ corresponds to 2,2-dimethylbutane • 23DMC ₄ corresponds to 2,3-dimethylbutane • 2MC ₅ corresponds to 2-methylpentane • 3MC ₅ corresponds to 3-methylpentane • nC ₆ corresponds to normal paraffin C ₆ • CC ₅ corresponds to cyclopentane • MCC ₅ corresponds to methylcyclopentane • CC ₆ corresponds to cyclohexane

Claims (5)

1. Process for the reduction of the benzene content of gasoline fractions, in which a hydrogenation is carried out in a hydrogenation zone, followed by an isomerization in an isomerization zone, of a feed with a weight composition within the following ranges :

   between 40 and 80% paraffins,

   between 0.5 and 7% naphthenes,

   between 6 and 45% aromatics

   and a maximum distillation temperature between 70 and 90°C, characterized in that the hydrogenation catalyst comprises at least one metal chosen from within the group formed by nickel, platinum and palladium, on a support, in that the isomerization catalyst comprises a zeolite and ac least one metal from group VIII, and in that the isomerization takes place at a temperature of between 230°C and 280°C.
2. Process according to claim 1, wherein the zeolite is a mordenite or an omega zeolite.
3. Process according to claim 1 or 2, wherein the metal of group VIII of the isomerization catalyst is chosen from the group constitued by platinum, palladium and nickel.
4. Process according to any one of the claims l to 3, wherein the hydrogenation takes place under the following operating conditions : the temperature is between 100 and 400°C, the pressure is between 1 and 60 bar, the liquid hourly space velocity is between 1 and 50 charge volumes per volume of catalyst and per hour and the hydrogen flow rate is between 1 and 2000 volumes per catalyst volume and per hour.
5. Process according to any one of the claims l to 4, wherein the isomerization takes place at a hydrogen partial pressure of between atmospheric pressure and 70 bar, a liquid hourly space velocity of between 0.2 and 10 litres of charge par litre of catalyst and per hour and the molar ratio of hydrogen to feed of between 0.5 and 10.

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