EP0552070A1 - Lowering of the benzene content in gasolines - Google Patents

Abstract

Process for reducing the content of benzene in petrol fractions in which a hydrogenation is performed of the feedstock characterised by: a weight composition included within the following ranges: - between 40 and 80 % of paraffins, - between 0.5 and 7 % of naphthenes, - between 6 and 45 % of aromatics and a maximum distillation temperature of between 70 and 90 DEG C, followed by an isomerisation of the effluent originating from the hydrogenation, the process being characterised in that a C5-C6 cut has been mixed with the said feedstock and/or the said effluent. <IMAGE>

Description

The invention relates to a process allowing the reduction of the benzene content in gasoline fractions by a process combining the hydrogenation of the benzene contained in the light reformate and optionally the hydrogenation of a C₅-C₆ cut and the isomerization of the effluent from hydrogenation and possibly from said cut.

The environmental problems will lead jointly to the reduction of the lead content and to the reduction of the benzene content in gasoline fractions, preferably without reduction of octane number. This leads to the need for a rearrangement of the various hydrocarbons present in the gasoline fractions.

Catalytic reforming used under severe conditions, and isomerization of normal C₅-C₆ paraffins of low octane number are the most commonly used processes currently for obtaining high octane numbers without the addition of lead. 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 of separating the C₅-C₆ fraction from the reformate, isomerizing it and 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 treatment by isomerization of the C₅-C₆ cut resulting from the direct distillation of crude oil, is also well known. It leads to a considerable improvement in the octane number of said cut. 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 transforms 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 the hydroisomerization of cyclic hydrocarbons which uses a group VIII metal supported on zeolite as a catalyst for opening rings under 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 reduction in the octane number of the charge.

The object of the present invention is to carry out jointly the reduction of the benzene content contained in the light reformate and the isomerization of the paraffins contained on the one hand in this light reformate and on the other hand in a C₅-C₆ cut generally paraffinic and from direct distillation.

The process of the present invention therefore comprises the hydrogenation of the benzene contained in the feed defined below in a hydrogenation zone and then the isomerization of the effluent resulting from the hydrogenation in an isomerization zone, the process being characterized in that a C₅-C₆ cut is mixed with said charge and / or said effluent.

Surprisingly, the joint treatment in the isomerization zone of these two possibly hydrogenated charges leads to the production of an effluent almost completely free of benzene and having an octane number sufficiently high that it can be directly incorporated into essence fractions after stabilization.

The hydrogenation zone and the isomerization zone according to the invention can be included in the same reactor, or else 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 are carried out (namely the operating conditions, the catalyst, etc.) are the conditions known to those skilled in the art. They are nevertheless specified below.

• la fraction légère du réformat,
• une coupe C₅-C₆ généralement issue de la distillation directe.

The charges concerned by the present invention are generally the following:

• the slight fraction of the reformate,
• a C₅-C₆ cut generally resulting from direct distillation.

• paraffines : entre 40,0 et 80,0 %,
• naphtènes : entre 0,9 et 7,0 %,
• aromatiques : entre 6,0 et 45,0 %.

The light fraction of the reformate is obtained by distillation of the said reformate. The maximum distillation temperature of this fraction is between 70 and 90 ° C, preferably between 77 and 83 ° C. The weight composition by hydrocarbon families of this light fraction of the reformate is variable according to the following intervals:

• paraffins: between 40.0 and 80.0%,
• naphthenes: between 0.9 and 7.0%,
• aromatic: between 6.0 and 45.0%.

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

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

• 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 generally 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 / cm³,
• the value of the research octane number is generally between 75 and 90.

Any other hydrocarbon feedstock from another process or set of processes and having characteristics similar to those described above can also be used.

The weight composition of the C₅-C₆ cut generally resulting from direct distillation, is variable. It depends on the nature of the crude to be treated in the case where the C₅-C₆ cut is obtained from direct distillation.

It may contain very low contents of compounds containing 4 carbon atoms per molecule (less than 0.5% by weight).

The paraffin content of said cut is generally greater than 90% by weight, its naphthene content generally less than 10% by weight and the benzene content generally less than 1.5% by weight. Its research octane number is generally between 60 and 75.

These two types of charge can be sent together to the hydrogenation zone, the light reformate content of the charge entering the hydrogenation zone being between 10 and 90% and preferably between 20 and 80%.

Preferably, the C₅-C₆ cut is mixed with the effluent from the hydrogenation, that is to say with the saturated light reformate leaving the hydrogenation zone, the effluent content from the hydrogenation of the charge entering the isomerization zone being between 10 and 90% and preferably between 20 and 80%.

Whatever the load envisaged, the pressure required for this hydrogenation stage is generally between 1 and 60 bar absolute, particularly between 2 and 50 bar and more advantageously between 5 and 45 bar.

The operating temperature is generally between 100 and 400 ° C, more advantageously between 150 and 350 ° C and preferably between 160 and 320 ° C.

The space velocities calculated with respect to the catalyst are generally 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 generally between 1 and 2000 volumes (gas under normal conditions) per volume of catalyst and per hour.

Advantageously, the heat released at this stage is used to preheat the charge of the isomerization.

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

When using platinum or palladium, the catalyst can advantageously contain at least one halogen in a proportion by weight relative to the catalyst of between 0.5 and 2%. Preferably, chlorine or fluorine or a combination of the two is used in a proportion relative to the total weight of catalyst of 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 the metal M by relative to the total weight of catalyst is between 0.1 and 10% and preferably between 0.05 and 5%.

The support can be chosen from the group formed by alumina, silica-aluminas, silica, zeolites, activated carbon, clays and aluminous cements. An alumina is preferably used, with a specific surface at least equal to 50 m² / g and with a pore volume at least equal to 0.4 cm³ / g, for example with a specific surface of between 50 and 350 m² / g and with a pore volume included between 0.4 and 1.2 cm³ / g.

The effluent from the hydrogenation zone generally contains less than 0.1% of aromatics and generally has between 4 and 6 points of octane index less than the feed entering this zone.

The isomerization zone is supplied by the effluent from the hydrogenation zone alone, comprising the light reformate mixture plus the hydrogenated C₅-C₆ cut, or by a light reformate mixture plus non-hydrogenated C₅-C₆ cut. The isomerization is generally carried out in said isomerization zone under the following usual conditions: the temperature is between 150 ° C and 300 ° C and preferably between 230 and 280 ° C, and the partial pressure of hydrogen is between atmospheric pressure and 70 bar and preferably between 5 and 50 bar. The space velocity is between 0.2 and 10 liters and preferably between 0.5 and 5 liters of liquid hydrocarbons per liter of catalyst per hour. The hydrogen / charge molar ratio is normally between 0.5 and 10 and preferably between 1 and 3.

The catalyst used in the isomerization zone according to the process of the present invention can be a catalyst based on platinum on chlorinated alumina, said alumina containing from 1 to 10% of chlorine and preferably from 2 to 9% of chlorine, but preferably using 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. A mordenite having a 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 less than 0.1% (relative to the weight of dry zeolite), a volume of mesh V of the elementary mesh between 2.78 and 2 , 73 nm³ and preferably between 2.77 and 2.74 nm³, a benzene absorption capacity 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, ...) 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, or in the form of acid. hexachloroplatinic in the case of platinum or either in the 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 effluent obtained at the exit from the isomerization zone has an octane number sufficiently high to be incorporated into the gasoline fractions after stabilization and comprises a maximum benzene content generally equal to 0.1% by weight. Preferably, it is completely free of benzene.

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

The stabilized reformate (1) is sent to a distillation column (6), from which a heavy reformate (3) is extracted at the bottom which can be used directly in the gasoline fractions and at the head a light reformate (2). The latter is sent to a hydrogenation unit (7), alone or after mixing with at least one part (9) of a C₅-C₆ cut from direct distillation. The cut obtained (4) is treated in an isomerization unit (8) giving the final product (5) which, after stabilization, can be incorporated into the gasoline fractions. Optionally at least part (10) of the C₅-C₆ direct distillation section is mixed with the saturated light reformate (4) just before the isomerization unit (10).

The two examples which follow specify the invention without limiting its scope. The hydrogenation and isomerization reactions are carried out in said examples in two separate reactors (or units).

Example 1 (according to the invention)

The light reformate obtained after distillation at 85 ° C, containing 21.5% of benzene and having an octane number of 80.3 is mixed in an amount of 50% by weight with a C₅-C₆ cut of direct distillation containing 0.7 % of benzene and having an octane number of 65. The compositions of these 2 products are listed in Table I. The charge from the mixture, the composition of which also appears 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 is 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 70.9. It is then sent to an isomerization unit operating at a temperature of 260 ° C, a pressure of 30 bar with an LHSV equal to 2 h⁻¹ and a hydrogen to hydrocarbon molar ratio of the charge of the isomerization unit equal to 4. The catalyst used in the isomerization unit contains 0.3% of Pt deposited on a support composed of 80% of mordenite with Si / Al ratio = 11 and 20% of alumina. The effluent leaving the isomerization unit has the composition given in Table I; he ... not contains more benzene and has an octane number of 78.1. It can therefore be directly incorporated into the gasoline fractions after stabilization. Reformate C₅-C₆ distillation cup Charge of hydrogenation Hydrogenation effluent Isomerization effluent light 6.5 1.0 3.7 3.7 4.6 iC5 9.9 18.9 14.4 14.4 18.8 nC5 7.1 25.4 16.25 16.25 12.5 22DMC4 3.0 0.4 1.7 1.7 6.3 23DMC4 4.1 1.85 3.0 3.0 4.8 2MC5 15.8 11.1 13.45 13.45 17.6 3MC5 12.5 9.4 11.0 11.0 11.55 nC6 12.1 19.6 15.9 15.9 8.75 C7 3.5 4.4 3.9 3.9 1.9 CC5 0.4 1.4 0.9 0.9 0.9 MCC5 3.6 4.1 3.85 3.85 9.9 Benzene 21.5 0.7 11.1 - - CC6 0 1.75 0.85 11.95 2.4 RON 80.3 65 72.9 70.9 78.1 Table I

Example 2 (according to the invention)

The light reformate obtained after distillation at 85 ° C. containing 21.5% benzene, having an octane number of 80.3 and the detailed composition of which is given in Table II, 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 is 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 II, no longer contains benzene but has an octane number of 76.5. It is then mixed in an amount of 50% by weight with a C₅-C₆ cut of direct distillation containing 0.7% of benzene and having an octane number of 65. The composition of this cut as well as the composition of the mixture which constitutes the load of the isomerization unit are given in table II. The isomerization unit operates at a temperature of 260 ° C., a pressure of 30 bar with an LHSV equal to 2 and a hydrogen to hydrocarbon molar ratio of the charge equal to 4. The catalyst used in this isomerization unit contains 0.3% Pt 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 II; it no longer contains benzene and has an octane number of 78.1. This effluent can be directly incorporated into the gasoline fractions after stabilization. Reformate C₅-C₆ distillation cup Hydrogenation effluent Charging the isomerization Isomerization effluent light 6.5 1.0 6.5 3.7 4.6 iC5 9.9 18.9 9.9 14.4 18.8 nC5 7.1 25.4 7.1 16.25 12.5 22DMC4 3.0 0.4 3.0 1.7 6.3 23DMC4 4.1 1.85 4.1 3.0 4.8 2MC5 15.8 11.1 15.8 13.45 17.6 3MC5 12.5 9.4 12.5 11.0 11.55 nC6 12.1 19.6 12.1 15.9 8.75 C7 3.5 4.4 3.5 3.9 1.9 CC5 0.4 1.4 0.4 0.9 0.9 MCC5 3.6 4.1 3.6 3.85 9.9 Benzene 21.5 0.7 - 0.35 - CC6 0 1.75 21.5 11.6 2.4 RON 80.3 65 76.5 71.2 78.1 Table II

Claims (8)

1 - Process for reducing the benzene content in gasoline fractions in which a hydrogenation of the charge is carried out in a hydrogenation zone, characterized by:
a weight composition in 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,
then an isomerization, in an isomerization zone, of the effluent resulting from the hydrogenation, the process being characterized in that a C₅-C₆ cut is mixed at least with one of the following hydrocarbon cuts: . said charge, . said effluent. 2 - Process according to claim 1 wherein the mixture comprises 10 to 90% of said hydrocarbon fraction. 3 - Method according to one of claims 1 or 2 wherein the hydrogenation catalyst comprises at least one metal selected from the group formed by nickel, platinum and palladium. 4 - Method according to one of claims 1 to 3 wherein the isomerization catalyst comprises a mordenite of Si / Al ratio between 5 and 50 and at least one group VIII metal. 5 - Process according to claim 4 wherein the metal of group VIII is chosen from the group formed by platinum, palladium and nickel. 6 - Method according to one of claims 1 to 5 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 space speed is between 1 and 50 volumes of feed per volume of catalyst and per hour and the hydrogen flow rate is between 1 and 2000 volumes per volume of catalyst and per hour. 7 - Method according to one of claims 1 to 6 wherein the isomerization is done according to the following operating conditions: the temperature is between 150 and 300 ° C, the partial hydrogen pressure is between atmospheric pressure and 70 bar, the space velocity is between 0.2 and 10 liters of charge per liter of catalyst and per hour, and the hydrogen to charge molar ratio is between 0.5 and 10. 8.- Method according to one of claims 1 to 7 wherein the C₅-C₆ cut is a direct distillation cut.

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