EP1406990B1 - Method for production of medium distillates by hydroisomerisation and hydrocracking in two stages of material from the fischer-tropsch process - Google Patents

Description

The present invention relates to a process and a treatment plant with hydrocracking and hydroisomerization, feedstock from the Fischer-Tropsch process, for obtaining middle distillates (gas oil, kerosene).

In the Fischer-Tropsch process, the synthesis gas (CO + H ₂ ) is catalytically converted into oxygenates and substantially linear hydrocarbons in gaseous, liquid or solid form. These products are generally free of heteroatomic impurities such as, for example, sulfur, nitrogen or metals. They also contain practically little or no aromatics, naphthenes and more generally cycles especially in the case of cobalt catalysts. On the other hand, they may have a significant content of oxygenated products which, expressed by weight of oxygen, is generally less than about 5% by weight and also an unsaturated content (olefinic products in general) generally less than 10% by weight. However, these products, mainly paraffins normal, can not be used as such, in particular because of their cold-holding properties not compatible with the usual uses of oil cuts. For example, the pour point of a linear hydrocarbon containing 20 carbon atoms per molecule (boiling point equal to about 340 ° C., that is to say often included in the middle distillate cut) is +37 ° C about what makes its use impossible, the specification being -15 ° C for diesel. The hydrocarbons resulting from the Fischer-Tropsch process comprising mainly n-paraffins must be converted into more valuable products such as, for example, gas oil, kerosene, which are obtained after catalytic reactions of hydroisomerization.

The patent EP-583,836 discloses a process for the production of middle distillates from filler obtained by Fischer-Tropsch synthesis. In this process, the filler is treated in its entirety, at most it is possible to remove the fraction C ₄ minus and obtain the fraction C ₅ ⁺ boiling at near 100 ° C. Said feed is subjected to a hydrotreatment and then to a hydroisomerisation with a conversion (products boiling above 370 ° C in lower boiling products) by at least 40% by weight. A catalyst that can be used in hydroconversion is a platinum-silica-alumina formulation. The conversions described in the examples are at most 60% by weight.

1. a) passage de la charge sur un premier catalyseur d'hydroisomérisation/hydrocraquage, qui est un catalyseur amorphe contenant au moins un métal noble du groupe VIII,
2. b) distillation de l'effluent hydroisomérisé/hydrocraqué pour obtenir des distillats moyens et une fraction résiduelle bouillant au-dessus des distillats moyens,
3. c) sur un second catalyseur d'hydroisomérisation/hydrocraquage, qui est un catalyseur amorphe contenant au moins un métal noble du groupe VIII, passage de la fraction lourde résiduelle et distillation de l'effluent pour obtenir des distillats moyens.

The publication EP-A-0321303 discloses a process for producing middle distillates from a paraffinic feedstock produced by Fischer-Tropsch synthesis, comprising the steps of:

1. a) passing the feedstock over a first hydroisomerization / hydrocracking catalyst, which is an amorphous catalyst containing at least one noble metal of group VIII,
2. b) distillation of the hydroisomerized / hydrocracked effluent to obtain middle distillates and a residual fraction boiling over the middle distillates,
3. c) on a second hydroisomerization / hydrocracking catalyst, which is an amorphous catalyst containing at least one noble metal of group VIII, passage of the residual heavy fraction and distillation of the effluent to obtain middle distillates.

The document US 6153087 mentions that in a similar process for the treatment of heavy crude oil, middle distillates may be recycled.

The present invention provides an alternative process for the production of middle distillates without the production of oils.

• d'améliorer fortement les propriétés à froid des paraffines issues du procédé Fisher-Tropsch et ayant des points d'ébullition correspondants à ceux des fractions gazole et kérosène (encore appelés distillats moyens) et notamment d'améliorer le point de congélation des kérosène,.
• d'augmenter la quantité de distillats moyens disponibles par hydrocraquage des composés paraffiniques les plus lourds, présents dans l'effluent de sortie de l'unité Fischer-Tropsch, et qui ont des points d'ébullition supérieurs à ceux des coupes kérosène et gazole, par exemple la fraction 380°C⁺.

This process allows:

• to strongly improve the cold properties of paraffins from the Fisher-Tropsch process and having boiling points corresponding to those of diesel and kerosene fractions (also called middle distillates) and in particular to improve the freezing point of kerosene ,.
• to increase the amount of available middle distillates by hydrocracking the heavier paraffinic compounds present in the outlet effluent of the Fischer-Tropsch unit, and which have boiling points higher than those of the kerosene and diesel fractions, for example the fraction 380 ° C ⁺ .

• a) éventuel fractionnement de l'effluent en au moins une fraction lourde à point d'ébullition initial compris entre 120 et 200°C, et au moins une fraction légère bouillant en-dessous de ladite fraction lourde,
• b) éventuel hydrotraitement d'une partie au moins de l'effluent ou de la fraction lourde, éventuellement suivi (étape c) d'élimination d'au moins une partie de l'eau,
• d) passage d'une partie au moins de l'effluent ou de la fraction éventuellement hydrotraité sur un premier catalyseur d'hydroisomérisation / hydrocraquage qui est un catalyseur amorphe contenant au moins un métal noble du groupe VIII,
• e) distillation de l'effluent hydroisomérisé / hydrocraqué pour obtenir des distillats moyens (kérosène, gasoil) et une fraction résiduelle bouillant au-dessus des distillats moyens,
• f) sur un second catalyseur d'hydroisomérisation / hydrocraquage qui est un catalyseur amorphe contenant au moins un métal noble du groupe VIII, passage d'une partie de ladite fraction lourde résiduelle et/ou d'une partie desdits distillats moyens, et distillation de l'effluent résultant pour obtenir des distillats moyens.

More specifically, the invention relates to a process for the production of middle distillates from a paraffinic effluent produced by Fischer-Tropsch synthesis, comprising the following successive stages:

• a) optionally fractionating the effluent into at least one heavy fraction with an initial boiling point of between 120 and 200 ° C, and at least one light fraction boiling below said heavy fraction,
• b) optional hydrotreatment of at least part of the effluent or heavy fraction, possibly followed (step c) of elimination of at least part of the water,
• d) passing at least a portion of the effluent or the optionally hydrotreated fraction onto a first hydroisomerization / hydrocracking catalyst which is an amorphous catalyst containing at least one noble metal of group VIII,
• e) distillation of the hydroisomerized / hydrocracked effluent to obtain middle distillates (kerosene, gas oil) and a residual fraction boiling over the middle distillates,
• f) on a second hydroisomerization / hydrocracking catalyst which is an amorphous catalyst containing at least one noble metal of group VIII, passage of a part of said residual heavy fraction and / or a part of said middle distillates, and distillation of the resulting effluent to obtain middle distillates.

1. a) De préférence, l'effluent paraffinique issu de l'unité de synthèse Fischer-Tropsch est fractionné en au moins deux fractions. Il est séparé de la charge une (ou plusieurs) fractions légères pour obtenir une fraction lourde ayant un point d'ébullition initial égal à une température comprise entre 120 et 200°C et de préférence entre 130 et 180°C et par exemple environ 150°C, la fraction légère bouillant en-dessous de la fraction lourde. La fraction lourde présente généralement des teneurs en paraffines d'au moins 50% pds, et le plus souvent d'au moins 90% pds.
2. b) Eventuellement ladite fraction lourde est, en présence d'hydrogène, mise en contact avec un catalyseur d'hydrotraitement. En l'absence de l'étape a), l'effluent issu de l'unité de synthèse Fischer-Tropsch est traité sur le catalyseur d'hydrotraitement.
3. c) Eventuellement, l'eau formée durant l'étape d'hydrotraitement (b) est éliminée au moins en partie et de préférence en totalité.
4. d) Au moins une partie (et de préférence la totalité) de l'effluent issu de l'étape (c) ou (b) est mis en contact en présence d'hydrogène et d'un catalyseur d'hydroisomérisation / hydrocraquage pour produire des distillats moyens, la conversion de produits 370°C⁺ en 370°C^- étant supérieure à 80% pds.
5. e) L'effluent en sortie de l'étape (d) est soumis à une étape de séparation dans un train de distillation de manière à séparer :
   • les produits légers inévitablement formés lors de l'étape (d) par exemple les gaz (C1-C4) et une coupe essence et également de manière à distiller au moins une coupe gazole et également au moins une coupe kérosène, et également à distiller une fraction, dite fraction résiduelle, dont les composés qui la constituent ont des points d'ébullition supérieurs à ceux des distillats moyens (kérosène + gazole). Cette fraction non hydrocraquée (dite fraction résiduelle) présente généralement un point d'ébullition initial d'au moins 350°C, de préférence supérieure à 370°C.
6. f) Passage d'au moins un distillat moyen et/ou de la fraction résiduelle issu de l'étape (e) en présence d'hydrogène, sur un catalyseur d'hydroisomérisation /hydrocraquage (dit second catalyseur). Les conditions opératoires peuvent être identiques ou différentes de celles utilisées dans l'étape (d). Les catalyseurs peuvent être identiques ou différents de ceux de l'étape (d). L'effluent issu de l'étape (f) est alors recyclé en entrée du train de séparation étape (e).

In more detail, the steps are as follows:

1. a) Preferably, the paraffinic effluent from the Fischer-Tropsch synthesis unit is fractionated into at least two fractions. One (or more) light fractions are separated from the feed to obtain a heavy fraction having an initial boiling point equal to a temperature of between 120 and 200 ° C. and preferably between 130 and 180 ° C. and for example about 150 ° C. ° C, the light fraction boiling below the heavy fraction. The heavy fraction generally has paraffin contents of at least 50 wt%, and most often at least 90 wt%.
2. b) If necessary, said heavy fraction is, in the presence of hydrogen, brought into contact with a hydrotreatment catalyst. In the absence of step a), the effluent from the Fischer-Tropsch synthesis unit is treated on the hydrotreatment catalyst.
3. c) Optionally, the water formed during the hydrotreating step (b) is removed at least in part and preferably completely.
4. d) At least a portion (and preferably all) of the effluent from step (c) or (b) is contacted in the presence of hydrogen and a hydroisomerization / hydrocracking catalyst to produce middle distillates, the product conversion 370 ° C ⁺ 370 ° C ^- being greater than 80% wt.
5. e) The effluent leaving step (d) is subjected to a separation step in a distillation train so as to separate:
   • the light products inevitably formed during step (d), for example the gases (C1-C4) and a gasoline cut, and also so as to distil at least one gas oil cut and also at least one kerosene cut, and also to distil a fraction, called residual fraction, whose compounds constituting it have boiling points higher than those of middle distillates (kerosene + gas oil). This non-hydrocracked fraction (called residual fraction) generally has an initial boiling point of at least 350 ° C., preferably greater than 370 ° C.
6. f) Passage of at least one middle distillate and / or the residual fraction from step (e) in the presence of hydrogen, on a hydroisomerization / hydrocracking catalyst (said second catalyst). The operating conditions can be identical to or different from those used in step (d). The catalysts may be the same or different from those of step (d). The effluent from step (f) is then recycled to the input of the separation step (e).

Unexpectedly, the use of a method according to the invention has revealed many advantages. In particular, it has been found that it is advantageous not to treat the light hydrocarbon fraction of the Fischer Tropsch effluent, a light fraction which comprises in terms of boiling points a gasoline fraction (C ₅ at most 200 ° C. and most often at about 150 ° C).

Indeed, unexpectedly the results obtained show that it is more profitable to send said gasoline cut (C ₅ to at most 200 ° C) to a steam cracker to make olefins that to treat it in the process according to the invention, where it has been found that the quality of this cut is only slightly improved. In particular, its engine and search octane numbers remain too low for this cut to be integrated into the gasoline pool. Thus, the process according to the invention allows the production of middle distillates (kerosene, diesel) with a minimum of gasoline obtained. Furthermore, the yields of middle distillates (kerosene + gas oil) of the process according to the invention are higher than those of the prior art, in particular because the kerosene cut (generally initial boiling point of 150 to 160 ° C. - final boiling point of 260 to 280 ° C) could be optimized (even maximized compared to the prior art), and more, without detriment to the diesel cut. Moreover, this kerosene cut unexpectedly has excellent cold properties (freezing point for example).

On the other hand, the fact of not treating the light fraction of the Fischer-Tropsch effluent makes it possible to minimize the volumes of the hydrotreatment and hydroisomerization / hydrocracking catalysts to be used and thus to reduce the size of the reactors and thus the investments.

Moreover, and unexpectedly, the catalytic performances (activity, selectivity) and / or the cycle time of the hydrotreatment and hydroisomerization / hydrocracking catalysts used in the process according to the invention could be improved.

Finally, unexpectedly the use of independent hydroisomerization / hydrocracking zones makes it possible to obtain higher yields of middle distillates and, for a given yield of middle distillates, better product qualities than the processes of the prior art. and in particular with regard to the cold properties. Furthermore, the flexibility of the process that is obtained because of the existence of these two separate zones allows the operator to modulate the operating conditions according to the qualities and / or yields of middle distillates to obtain.

Detailed description of the invention

The description will be made with reference to the Figures 1 and 2 which represent 2 embodiments of the invention.

Step a)

The effluent from the Fischer-Tropsch synthesis unit comprises mainly paraffins but also contains olefins and oxygenated compounds such as alcohols. It also contains water, CO ₂ , CO and unreacted hydrogen as well as light hydrocarbon compounds C1 to C4 in the form of gas. When this step is carried out, the effluent from the Fischer-Tropsch synthesis unit is fractionated (for example by distillation) into at least two fractions: at least one light fraction and at least one heavy-point fraction. initial boiling equal to a temperature between 120 and 200 ° C and preferably between 130 and 180 ° C and even more preferably at a temperature of about 150 ° C, in other words the cutting point is between 120 and 200 ° C.

The heavy fraction generally has paraffin contents of at least 50% by weight.

This fractionation can be carried out by methods well known to those skilled in the art such as flash, distillation, etc. As a non-limiting example, the effluent from the Fischer-Tropsch synthesis unit will be subject to flash, decantation to remove water and distillation to obtain at least the 2 fractions described above.

The light fraction is not treated according to the process of the invention but may for example constitute a good load for petrochemicals and more particularly for a steam cracking unit. At least one heavy fraction previously described is treated according to the method of the invention.

Step b)

Optionally, this fraction or at least part of the initial charge is admitted via line (1) in the presence of hydrogen (supplied via line (2)) to an area (3) containing a hydrotreatment catalyst which has aim is to reduce the content of olefinic and unsaturated compounds as well as to hydrotreat the oxygenates (alcohols) present in the heavy fraction described above.

The catalysts used in this step (b) are hydrotreating catalysts which are non-crunchy or slightly crisp and comprise at least one metal of group VIII and / or group VI of the periodic table of elements. Preferably, the catalyst comprises at least one metal of the metal group formed by nickel, molybdenum, tungsten, cobalt, ruthenium, indium, palladium and platinum and comprising at least one support.

The hydro-dehydrogenating function is preferably provided by at least one metal or group VIII metal compound such as nickel and cobalt in particular. A combination of at least one metal or group VI metal compound (especially molybdenum or tungsten) and at least one metal or group VIII metal compound (especially cobalt and nickel) of the classification may be used periodic elements. The non-noble group VIII metal concentration, when used, is 0.01-15% by weight based on the finished catalyst.

Advantageously, at least one element selected from P, B, Si is deposited on the support.

This catalyst may advantageously contain phosphorus; indeed, this compound brings two advantages to hydrotreatment catalysts: an ease in particular during the impregnation of the nickel and molybdenum solutions, and a better hydrogenation activity.

In a preferred catalyst, the total concentration of metals of groups VI and VIII, expressed as metal oxides, is between 5 and 40% by weight and preferably between 7 and 30% by weight and the weight ratio expressed as metal oxide. (or metals) of group VI on metal (or metals) of group VIII is between 1.25 and 20 and preferably between 2 and 10. Advantageously, if there is phosphorus, the concentration of phosphorus oxide P2O5 will be lower 15% by weight and preferably less than 10% by weight.

It is also possible to use a catalyst containing boron and phosphorus. Advantageously, boron and phosphorus are promoter elements deposited on the support, and for example the catalyst according to the patent. EP-297.949 . The sum of the amounts of boron and phosphorus, expressed respectively by weight of boron trioxide and phosphorus pentoxide, relative to the weight of support, is about 5 to 15% and the atomic ratio boron on phosphorus is about 1 1 to 2: 1 and at least 40% of the total pore volume of the finished catalyst is contained in pores with an average diameter greater than 13 nanometers. Preferably, the amount of Group VI metal such as molybdenum or tungsten is such that the phosphorus atomic ratio on Group VIB metal is about 0.5: 1 to 1.5: 1; the amounts of Group VIB metal and Group VIII metal, such as nickel or cobalt, are such that the atomic ratio of Group VIII metal to Group VIB metal is about 0.3: 1 to 0.7 1. The amounts of Group VIB metal expressed in weight of metal relative to the weight of finished catalyst is about 2 to 30% and the amount of Group VIII metal expressed as weight of metal relative to the weight of finished catalyst is about 0.01 to 15%.

The Ni alumina, NiMo on alumina, NiMo on alumina doped with boron and phosphorus and NiMo on silica-alumina catalysts are also preferred. Advantageously, eta or gamma alumina will be chosen.

Another particularly advantageous catalyst contains promoter silicon deposited on the support. An interesting catalyst contains BSi or PSi.

In the case of the use of noble metals (platinum and / or palladium) preferably, the metal content is between 0.05 and 3% by weight relative to the finished catalyst and preferably between 0.1 and 2% by weight. catalyst.
These metals are deposited on a support which is preferably an alumina, but which may also be boron oxide, magnesia, zirconia, titanium oxide, a clay or a combination of these oxides. These catalysts can be prepared by any method known to those skilled in the art or can be acquired from companies specializing in the manufacture and sale of catalysts.

In the hydrotreatment reactor (3), the feedstock is contacted in the presence of hydrogen and the catalyst at operating temperatures and pressures for carrying out the hydrodeoxygenation (HDO) of the alcohols and the hydrogenation of the olefins present in the load. The reaction temperatures used in the hydrotreatment reactor are between 100 and 350, preferably between 150 and 300 ° C, even more preferably between 150 and 275 ° C and more preferably between 175 and 250 ° C. The total pressure range used varies from 5 to 150 bar, preferably from 10 to 100 bar and even more preferably from 10 to 90 bar. The hydrogen that feeds the hydrotreatment reactor is introduced at a rate such that the volume ratio hydrogen / hydrocarbons is between 100 to 3000 Nl / l / h, preferably between 100 and 2000Ml / l / h and even more preferred between 250 and 1500 Nl / l / h. The charge rate is such that the hourly volume velocity is between 0.1 and 10 h ^-1 , preferably between 0.2 and 5 h ^-1 and even more preferably between 0.2 and 3 h ^-1 . Under these conditions, the content of unsaturated and oxygenated molecules is reduced to less than 0.5% and to less than 0.1% in general. The hydrotreatment step is conducted under conditions such that conversion to products having boiling points greater than or equal to 370 ° C to products having boiling points below 370 ° C is limited to 30% wt. preferably, less than 20% and even more preferably less than 10%.

Step c)

The effluent (line 4) from the hydrotreating reactor (3) is optionally introduced into a zone (5) of water removal which is intended to eliminate at least partly the water produced during the hydrotreatment reactions. This removal of water can be carried out with or without eliminating the C ₄ less gas fraction which is generally produced during the hydrotreating step. The elimination of water is understood to mean the elimination of the water produced by the hydrodeoxygenation (HDO) reactions of the alcohols, but it may also include the elimination at least partly of the saturation water of the hydrocarbons. The removal of water can be carried out by all the methods and techniques known to those skilled in the art, for example by drying, passage on a desiccant, flash, decantation ....

Step d)

At least part and preferably all of the hydrocarbon fraction (at least part of the feed or at least part of the heavy fraction of step a) or at least part of the hydrotreated fraction or feed and optionally dried) is then introduced (line 6) and possibly a stream of hydrogen (line 7) into the zone (8) containing said first hydroisomerization / hydrocracking catalyst. Another possibility of the process also according to the invention consists in sending part or all of the effluent leaving the hydrotreating reactor (without drying) into the reactor containing the hydroisomerization / hydrocracking catalyst and preferably at the same time. time as a flow of hydrogen.

The catalysts used in the hydroisomerization / hydrocracking step will be described later in detail.

Before use in the reaction, the metal contained in the catalyst must be reduced. One of the preferred methods for conducting the reduction of the metal is hydrogen treatment at a temperature of from 150 ° C to 650 ° C and a total pressure of 0.1 to 25 MPa. For example, a reduction consists of a stage at 150 ° C. for 2 hours then a rise in temperature up to 450 ° C. at the rate of 1 ° C./min and then a plateau of 2 hours at 450 ° C. throughout this reduction step, the hydrogen flow rate is 1000 liters hydrogen / liter catalyst. Note also that any ex-situ reduction method is suitable.

• La pression est maintenue entre 2 et 150 bars et de préférence entre 5 et 100 bars et avantageusement de 10 à 90 bars, la vitesse spatiale est comprise entre 0,1 h^-1 et 10 h^-1 et de préférence entre 0,2 et 7h^-1 est avantageusement entre 0,5 et 5,0h^-1. Le taux d'hydrogène est compris entre 100 et 2000 Normaux litres d'hydrogène par litre de charge et par heure et préférentiellement entre 150 et 1500 litres d'hydrogène par litre de charge.

The operating conditions in which this step (d) is carried out are:

• The pressure is maintained between 2 and 150 bar and preferably between 5 and 100 bar and advantageously from 10 to 90 bar, the space velocity is between 0.1 h ^-1 and 10 h ^-1 and preferably between 0.2 and 7h ^-1 is advantageously between 0.5 and 5,0h ^-1. The hydrogen content is between 100 and 2000 normal liters of hydrogen per liter of filler and per hour and preferably between 150 and 1500 liters of hydrogen per liter of filler.

The temperature used in this stage is between 200 and 450.degree. C. and preferably from 250.degree. C. to 450.degree. C., advantageously from 300 to 450.degree. C., and even more advantageously above 320.degree. C. or, for example, between 320.degree.-420.degree. .

The two stages, hydrotreatment and hydroisomerization-hydrocracking, can be carried out on the two types of catalysts in two or more different reactors, and / or in the same reactor.

Step e)

The hydroisomerized / hydrocracked effluent leaving the reactor (8), step (d), is sent to a distillation train (9) which incorporates an atmospheric distillation and optionally a vacuum distillation which is intended to separate the conversion products. of boiling point below 340 ° C and preferably below 370 ° C and including including those formed in step (d) in the reactor (8), and to separate the residual fraction whose initial point of boiling is generally greater than at least 340 ° C and preferably greater than or equal to at least 370 ° C. Among the conversion products and hydroisomerized it is separated, in addition to the light gases C1-C4 (line 10) at least a gasoline fraction (line 11), and at least a middle distillate fraction kerosene (line 12) and diesel (line 13) .

Step f)

The process according to the invention uses a second zone (16) containing a hydroisomerization / hydrocracking catalyst (called second catalyst). It passes on this catalyst, in the presence of hydrogen (line 15) an effluent chosen from a part of the kerosene produced (line 12), part of the gas oil (line 13) and the residual fraction and preferably the residual fraction whose initial boiling point is generally greater than at least 370 ° C.
The catalyst present in the reactor (16) of step (f) of the process according to the invention is in the same way as for stage d), of amorphous acid type and based on at least one noble metal of group VIII; however it may be the same or different from that of step d).

During this step, the fraction entering the reactor (16) undergoes, in the presence of hydrogen, hydroisomerization and / or hydrocracking reactions in the reactor, which will make it possible to improve the quality of the products formed and more particularly the properties cold kerosene and diesel, and obtain distillate yields improved over the prior art.

The choice of operating conditions makes it possible to finely adjust the quality of the products (middle distillates) and in particular the cold properties.

• La pression est maintenue entre 2 et 150 bars et de préférence entre 5 et 100 bars et avantageusement de 10 à 90 bars, la vitesse spatiale est comprise entre 0,1 h^-1 et 10 h^-1 et de préférence entre 0,2 et 7h^-1 est avantageusement entre 0,5 et 5,0h^-1. Le taux d'hydrogène est compris entre 100 et 2000 Normaux litres d'hydrogène par litre de charge et par heure et préférentiellement entre 150 et 1500 litres d'hydrogène par litre de charge.

The operating conditions in which this step (f) is carried out are:

• The pressure is maintained between 2 and 150 bar and preferably between 5 and 100 bar and advantageously from 10 to 90 bar, the space velocity is between 0.1 h ^-1 and 10 h ^-1 and preferably between 0.2 and 7h ^-1 is advantageously between 0.5 and 5,0h ^-1. The hydrogen content is between 100 and 2000 normal liters of hydrogen per liter of filler and per hour and preferably between 150 and 1500 liters of hydrogen per liter of filler.

The temperature used in this stage is between 200 and 450.degree. C. and preferably from 250.degree. C. to 450.degree. C., advantageously from 300 to 450.degree. C., and even more advantageously above 320.degree. C. or, for example, between 320.degree.-420.degree. .

The operator will adjust the operating conditions on the first and second hydrocracking / hydroisomerization catalyst so as to obtain the desired product qualities and yields.

Thus, in general, on the first catalyst, the conversion by pass in Products having a boiling point greater than or equal to 150 ° C. in products with a boiling point below 150 ° C. are less than 50% by weight, preferably less than 30% by weight. These conditions allow the individual to adjust the ratio of kerosene / diesel produced as well as the cold products of middle distillates, and more particularly kerosene.

Also generally, on the second catalyst, when the residual fraction is treated, the conversion by pass to products with boiling points greater than or equal to 370 ° C in products with boiling points lower than 370 ° C, is superior. at 40% by weight, preferably above 50% by weight, or better at 60% by weight. It can even be advantageous to have conversions of at least 80% by weight.

When a part of the kerosene and / or diesel fuel is treated on the second catalyst, the pass conversion into products with boiling points greater than or equal to 150 ° C into products with boiling points below 150 ° C is lower. at 50% by weight, preferably less than 30% by weight.

In general, the operating conditions applied in the reactors (8) and (16) may be different or identical. Preferably, the operating conditions used in the 2 hydroisomerization / hydrocracking reactors are chosen to be different in terms of operating pressure, temperature, contact time (wh) and H ₂ / feed ratio. This embodiment allows the operator to adjust the qualities and / or yields of kerosene and diesel.

The effluent from the reactor (16) is then sent via line (17) in the distillation train so as to separate the conversion products, gasoline, kerosene and diesel.

On the figure 1 , there is shown an embodiment with the residual fraction (line 14) passing through the hydroisomerization / hydrocracking zone (16) (step f), the effluent obtained being sent (line 17) to the zone (9) of separation.

Advantageously, at the same time, the kerosene and / or diesel fuel may be partly recycled (line 18) in the hydroisomerization / hydrocracking zone (8) (step d) on the first catalyst.

On the figure 2 a portion of the kerosene and / or diesel fuel produced passes into the hydroisomerization / hydrocracking zone (16) (step f), the resulting effluent being sent (line 17) to the separation zone (9).

At the same time, the residual fraction (line 14) is recycled to the hydroisomerization / hydrocracking zone (8) (step d) on the first catalyst.

It has been found that it is advantageous to recycle part of the kerosene on a hydrocracking / hydroisomerization catalyst to improve its cold properties.

In the figures, only the recycling of kerosene has been shown. It goes without saying that one can also recycle a portion of the gas oil (separately or with kerosene) and preferably on the same catalyst as kerosene.

The invention is not limited to these 2 embodiments.

The products obtained

The gas oil (s) obtained has a pour point of at most 0 ° C, generally below -10 ° C and often below -15 ° C. The cetane number is greater than 60, generally greater than 65, often greater than 70.

The resulting kerosene (s) has a freezing point of not more than -35 ° C, generally less than -40 ° C. The smoke point is greater than 25 mm, usually greater than 30 mm. In this process, the production of gasoline (not sought) is as low as possible. The yield of gasoline will always be less than 50% by weight, preferably less than 40% by weight; advantageously less than 30% by weight or 20% by weight or even 15% by weight.

• éventuellement au moins une zone d'hydrotraitement (3) d'un effluent paraffinique provenant d'une unité de synthèse Fischer-Tropsch,
• au moins une zone (8) contenant un premier catalyseur d'hydroisomérisation / hydrocraquage, munie d'une conduite (6) pour l'entrée d'une partie au moins de l'effluent éventuellement hydrotraité,
• au moins une colonne à distiller (9) munie des conduites (12, 13) pour la sortie des distillats moyens et (14) pour la sortie d'une fraction résiduelle bouillant au-dessus des distillats moyens,
• au moins une zone (16) contenant un second catalyseur
• d'hydroisomérisation / hydrocraquage, munie d'une conduite pour l'entrée de ladite fraction résiduelle et/ou d'une partie des distillats moyens, et d'une conduite (17) pour envoyer l'effluent obtenu dans la colonne (9).

The invention also relates to an installation for the production of middle distillates comprising:

• optionally at least one hydrotreatment zone (3) of a paraffinic effluent from a Fischer-Tropsch synthesis unit,
• at least one zone (8) containing a first hydroisomerization / hydrocracking catalyst, provided with a pipe (6) for the entry of at least a portion of the optionally hydrotreated effluent,
• at least one distillation column (9) provided with lines (12, 13) for the outlet of the middle distillates and (14) for the outlet of a residual fraction boiling over the middle distillates,
• at least one zone (16) containing a second catalyst
• hydroisomerization / hydrocracking device, provided with a pipe for the entry of said residual fraction and / or a part of the middle distillates, and a line (17) for sending the effluent obtained in the column (9) .

In an advantageous embodiment, the installation comprises a pipe (14) for sending said residual fraction into the zone (16) containing the second catalyst, and a pipe (18) for recycling a portion of the kerosene and / or diesel fuel produced in the zone (8) containing the first catalyst.

In another advantageous embodiment, the installation comprises a pipe (12, 13) for feeding a portion of the kerosene and / or diesel fuel produced in the zone (16) containing the second catalyst, and a pipe (14) for recycling. said residual fraction in the zone (8) containing the first catalyst.

Hydrocracking / hydroisomerization catalysts

The majority of catalysts currently used in hydroisomerization / hydrocracking are of the bifunctional type associating an acid function with a hydrogenating function. The acid function is provided by supports with large surface areas (generally 150 to 800 m ² .g ^-1 ) having a surface acidity, such as halogenated aluminas (chlorinated or fluorinated in particular), phosphorus aluminas, combinations of oxides of boron and aluminum, silica-aluminas. The hydrogenating function is provided either by one or more metals of group VIII of the periodic table of the elements, such as iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum, or by a combination of at least one Group VI metal such as chromium, molybdenum and tungsten and at least one Group VIII metal.

The equilibrium between the two acid and hydrogenating functions is the fundamental parameter which governs the activity and the selectivity of the catalyst. A weak acidic function and a strong hydrogenating function result in weakly active and selective catalysts in the isomerization whereas a strong acid function and a low hydrogenating function give very active and cracking-selective catalysts. A third possibility is to use a strong acid function and a strong hydrogenating function to obtain a very active catalyst but also very selective towards isomerization. It is therefore possible, by judiciously choosing each of the functions to adjust the activity / selectivity couple of the catalyst.
More specifically, the hydroisomerization-hydrocracking catalysts are bifunctional catalysts comprising an amorphous acid support (preferably a silica-alumina) and a hydro-dehydrogenating metal function provided by at least one noble metal.

The support is said to be amorphous, that is to say devoid of molecular sieves, and in particular of zeolite, as well as the catalyst. The amorphous acidic support is advantageously a silica-alumina but other supports are usable. When it is a silica-alumina, the catalyst preferably does not contain added halogen, other than that which could be introduced for the impregnation of the noble metal, for example. More generally, and preferably, the catalyst does not contain added halogen, for example fluorine. In general, and preferably, the support has not been impregnated with a silicon compound.

Several preferred catalysts are described below for use in the hydrocracking / hydroisomerization steps of the process according to the invention.

In a first preferred embodiment of the invention, a catalyst comprising a particular silica-alumina is used which makes it possible to obtain very active catalysts that are also very selective in the isomerization of effluents from Fischer-Synthesis units. Tropsch.

• un diamètre moyen des mésopores compris entre 1-12 nm,
• un volume poreux des pores dont le diamètre est compris entre le diamètre moyen tel que défini précédemment diminué de 3 nm et le diamètre moyen tel que défini précédemment augmenté de 3 nm est supérieur à 40 % du volume poreux total,
• une dispersion du métal noble comprise entre 20-100 %,
• un coefficient de répartition du métal noble supérieur à 0,1.

More specifically, the preferred catalyst comprises (and preferably consists essentially of) 0.05-10% by weight of at least one Group VIII noble metal deposited on an amorphous silica-alumina support (which preferably and 70% by weight of silica) which has a BET surface area of 100-500m ² / g and the catalyst has:

• an average diameter of the mesopores of between 1-12 nm,
• a pore volume of pores whose diameter is between the mean diameter as defined above decreased by 3 nm and the average diameter as defined above increased by 3 nm is greater than 40% of the total pore volume,
• a dispersion of the noble metal of between 20-100%,
• a distribution coefficient of the noble metal greater than 0.1.

• Le support préféré utilisé pour l'élaboration du catalyseur est composé de silice SiO₂ et d'alumine Al₂O₃. La teneur en silice du support, exprimée en pourcentage poids, est généralement comprise entre 1 et 95 %, avantageusement voire entre 5 et 95 % et de manière préférée entre 10 et 80 % et de manière encore plus préférée entre 20 et 70 % et entre 22 et 45 %. Cette teneur en silice est parfaitement mesurée à l'aide de la fluorescence X.

The characteristics of the catalyst are in more detail:

• The preferred support used for the production of the catalyst is composed of silica SiO ₂ and alumina Al ₂ O ₃ . The silica content of the support, expressed as a weight percentage, is generally between 1 and 95%, advantageously even between 5 and 95%, and preferably between 10 and 80% and even more preferably between 20 and 70%, and between 22 and 45%. This silica content is perfectly measured using X-ray fluorescence.

For this particular type of reaction, the metal function is provided by a noble metal of group VIII of the periodic table of elements and more particularly platinum and / or palladium.

The noble metal content, expressed in% by weight of metal relative to the catalyst, is between 0.05 to 10 and more preferably between 0.1 and 5.

The dispersion, representing the reagent-accessible metal fraction based on the total amount of catalyst metal, can be measured, for example, by H ₂ / O ₂ titration. The metal is reduced beforehand, that is to say that it undergoes treatment under hydrogen flow at high temperature under conditions such that all Hydrogen-accessible platinum atoms are converted to metallic form. Then, a flow of oxygen is sent under suitable operating conditions so that all the reduced platinum atoms accessible to oxygen is oxidized in PtO ₂ form. By calculating the difference between the quantity of oxygen introduced and the quantity of oxygen leaving, the quantity of oxygen consumed is reached; thus, it is possible to deduce from this latter value the amount of platinum accessible to oxygen. The dispersion is then equal to the ratio of the quantity of platinum accessible to oxygen to the total amount of platinum of the catalyst. In our case, the dispersion is between 20% and 100% and preferably between 30% and 100%.

The distribution of the noble metal represents the distribution of the metal within the catalyst grain, the metal being able to be well or poorly dispersed. Thus, it is possible to obtain the platinum poorly distributed (for example detected in a ring whose thickness is significantly less than the radius of the grain) but well dispersed that is to say that all the platinum atoms, located in crown, will be accessible to the reagents. In our case, the platinum distribution is good, that is to say that the platinum profile, measured according to the Castaing microprobe method, has a distribution coefficient greater than 0.1 and preferably greater than 0.1. 0.2.

The BET surface of the support is between 100 m ² / g and 500 m ² / g and preferably between 250 m ² / g and 450 m ² / g and for silica-alumina-based supports, even more preferably between 310 m ² / g and 450 m ² / g.

For the preferred silica-alumina catalysts the average pore diameter of the catalyst is measured from the porous distribution profile obtained with a mercury porosimeter. The average pore diameter is defined as the diameter corresponding to the cancellation of the derived curve obtained from the mercury porosity curve. The mean diameter of the pores, thus defined, is between 1 nm (1x10 ^-9 meters) and 12 nm (12x10 ^-9 meters) and preferably between 1 nm (1x10 ^-9 meters) and 11 nm (11x10 ^-9 meters). ) and even more preferably between 3 nm (4x10 ^-9 meters) and 10.5 nm (10.5x10 ^-9 meters).

The preferred catalyst has a porous distribution such as the pore volume of the pores whose diameter is between the mean diameter as defined previously decreased by 3 nm and the average diameter as defined above increased by 3 nm (ie the mean diameter ± 3 nm) is greater than 40% of the total pore volume and preferably between 50% and 90% of the total pore volume and more preferably between 50% and 70% of the total pore volume.

For the preferred silica-alumina catalyst it is generally less than 1.0 ml / g and preferably between 0.3 and 0.9 ml / g and even more preferably less than 0.85 ml / g.

The preparation and shaping of the support, and in particular of the silica-alumina (especially used in the preferred embodiment) is made by usual methods well known to those skilled in the art. Advantageously, prior to the impregnation of the metal, the support may undergo calcination, for example a heat treatment at 300-750 ° C. (preferred 600 ° C.) for 0.25-10 hours (preferred 2 hours) under 0. -30% volume of water vapor (for the silica alumina 7.5% preferred).

The noble metal salt is introduced by one of the usual methods used to deposit the metal (preferably platinum and / or palladium, platinum being still preferred) on the surface of a support. One of the preferred methods is dry impregnation which consists of introducing the metal salt into a volume of solution which is equal to the pore volume of the catalyst mass to be impregnated. Prior to the reduction operation, the catalyst may be calcined such as, for example, in dry air at 300-750 ° C (520 ° C preferred) for 0.25-10 hours (preferred 2 hours).

In a second preferred embodiment according to the invention, the bifunctional catalyst comprises at least one noble metal deposited on an amorphous acid support, the noble metal dispersion being less than 20%.

Preferably, the fraction of the noble metal particles having a size of less than 2 nm represents at most 2% by weight of the noble metal deposited on the catalyst.

Advantageously, at least 70% (preferably at least 80%, and more preferably at least 90%), noble metal particles have a size greater than 4 nm (% number).

The support is amorphous, it does not contain molecular sieve; the catalyst does not contain molecular sieves either.
The amorphous acid support is generally chosen from the group formed by a silica-alumina, a halogenated alumina (preferably fluorinated), a silicon-doped alumina (deposited silicon), a titanium oxide alumina mixture, a sulphated zirconia, a doped zirconia with tungsten, and mixtures thereof with one another or with at least one amorphous matrix chosen from the group formed by alumina, titanium oxide, silica, boron oxide, magnesia, zirconia, clay by example. Preferably, the support consists of an amorphous silica alumina.

A preferred catalyst comprises (preferably consists essentially of) from 0.05 to 10% by weight of at least one Group VIII noble metal deposited on an amorphous silica-alumina support.

• Le support préféré utilisé pour l'élaboration du catalyseur est composé de silice SiO₂ et d'alumine Al₂O₃ dès la synthèse. La teneur en silice du support, exprimée en pourcentage poids, est généralement comprise entre 1 et 95%, avantageusement entre 5 et 95% et de manière préférée entre 10 et 80% et de manière encore plus préférée entre 20 et 70% voire entre 22 et 45%. Cette teneur est parfaitement mesurée à l'aide de la-fluorescence X.

The characteristics of the catalyst are in more detail:

• The preferred support used for the preparation of the catalyst is composed of silica SiO ₂ and alumina Al ₂ O ₃ from the synthesis. The silica content of the support, expressed as a percentage by weight, is generally between 1 and 95%, advantageously between 5 and 95%, and preferably between 10 and 80% and even more preferably between 20 and 70%, or even between 20 and 70%. and 45%. This content is perfectly measured using X-fluorescence.

For this particular type of reaction, the metal function is provided by at least one noble metal of group VIII of the periodic table of elements and more particularly platinum and / or palladium.

The noble metal content, expressed in% by weight of metal relative to the catalyst, is between 0.05 to 10 and more preferably between 0.1 and 5.

The dispersion (measured in the same manner as above) is less than 20%, it is generally greater than 1% or better at 5%.

To determine the size and distribution of the metal particles we used Transmission Electron Microscopy. After preparation, the catalyst sample is finely ground in an agate mortar and is then ethanol-dispersed. Samples at different locations to ensure good representativeness in size are made and deposited on a copper grid covered with a thin carbon film. The grids are then air dried under infra-red light before being introduced into the microscope for observation. In order to estimate the average size of noble metal particles, several hundred measurements are made from dozens of shots. All of these measurements make it possible to produce a histogram of distribution of the particle size. Thus, we can accurately estimate the proportion of particles corresponding to each particle size domain.

The distribution of platinum is good that is to say that the platinum profile, measured according to the method of the microprobe of Castaing, has a distribution coefficient greater than 0.1 advantageously greater than 0.2 and preferably greater than 0.5.

The BET surface of the support is generally between 100 m ² / g and 500m ² / g and preferably between 250 m ² / g and 450 m ² / g and the silica alumina carriers, even more preferably 310 m ² / g.

For silica-based alumina supports, it is generally less than 1.2 ml / g and preferably between 0.3 and 1.1 ml / g and even more advantageously less than 1.05 ml / g.

The preparation and shaping of the silica-alumina and of any support in general is made by usual methods well known to those skilled in the art. Advantageously, prior to the impregnation of the metal, the support may undergo calcination, for example a heat treatment at 300-750 ° C. (600 ° C. preferred) for a period of between 0.25 and 10 hours (2 hours). preferred) under 0-30% volume of water vapor (about 7.5% preferred for a silica-alumina).

The metal salt is introduced by one of the usual methods used to deposit the metal (preferably platinum) on the surface of a support. One of the preferred methods is dry impregnation which consists of introducing the metal salt into a volume of solution which is equal to the pore volume of the catalyst mass to be impregnated. Prior to the reduction operation and to obtain the size distribution of the metal particles, the catalyst is calcined in humidified air at 300-750 ° C (550 ° C preferred) for 0.25-10 hours (preferred 2 hours). The partial pressure of H2O during the calcination is for example 0.05 bar to 0.50 bar (0.15 bar preferred). Other known methods of treatment making it possible to obtain the dispersion of less than 20% are suitable within the scope of the invention.

• une teneur pondérale en silice SiO₂ comprise entre 10 et 60% de préférence entre 20 et 60% et de manière encore plus préférée entre 20 et 50% poids ou 30-50% poids.
• une teneur en Na inférieure à 300 ppm poids et de préférence inférieure à 200 ppm poids,
• un volume poreux total compris entre 0.5 et 1.2 ml/g mesuré par porosimétrie au mercure,
• la porosité de ladite silice-alumine étant la suivante :
  1. i/ Le volume des mésopores dont le diamètre est compris entre 40Å et 150Å, et dont le diamètre moyen varie entre 80 et 120 Å représente entre 30 et 80% du volume poreux total précédemment défini et de préférence entre 40 et 70%.
  2. ii/ Le volume des macropores, dont le diamètre est supérieur à 500 Å, et de préférence compris entre 1000 Å et 10000 Å représente entre 20 et 80% du volume poreux total et de préférence entre 30 et 60% du volume poreux total et de manière encore plus préférée le volume des macropores représente au moins 35% du volume poreux total.
• une surface spécifique supérieure à 200 m²/g et de préférence supérieure à 250 m²/g.

Another preferred catalyst for the invention comprises at least one hydro-dehydrogenating element (preferably deposited on the support) and a support comprising (or preferably consisting of) at least one silica-alumina, said silica-alumina having the following characteristics: :

• a weight content of silica SiO ₂ of between 10 and 60%, preferably between 20 and 60% and even more preferably between 20 and 50% by weight or 30-50% by weight.
• an Na content of less than 300 ppm by weight and preferably less than 200 ppm by weight,
• a total pore volume of between 0.5 and 1.2 ml / g measured by mercury porosimetry,
• the porosity of said silica-alumina being as follows:
  1. The volume of the mesopores whose diameter is between 40Å and 150Å and whose mean diameter varies between 80 and 120Å represents between 30% and 80% of the total pore volume previously defined and preferably between 40% and 70%.
  2. ii / The volume of the macropores, whose diameter is greater than 500 Å, and preferably between 1000 Å and 10000 Å, represents between 20 and 80% of the total pore volume and preferably between 30 and 60% of the total pore volume and of even more preferably, the volume of the macropores represents at least 35% of the total pore volume.
• a specific surface area greater than 200 m ² / g and preferably greater than 250 m ² / g.

• Les diffractogrammes des silice-alumines de l'invention, obtenus par diffraction aux rayons X, correspondent à un mélange de la silice et de l'alumine avec une certaine évolution entre l'alumine gamma et la silice en fonction de la teneur en SiO₂ des échantillons. Dans ces silice-alumines on observe une alumine moins bien cristallisée par rapport à l'alumine seule.
• Les spectres du RMN de ²⁷Al des silice-alumines montrent deux massifs de pics distincts. Chaque massif peut être décomposé en au moins deux espèces. Nous observons une large domination des espèces dont le maximum résonne vers 10 ppm et qui s'étend entre 10 et 60 ppm. La position du maximum suggère que ces espèces sont essentiellement de type Al_VI (octaédrique). Sur tous les spectres nous observons un deuxième de type d'espèce qui résonne vers 80-110 ppm. Ces espèces correspondraient aux atomes d'AI_IV (tétraédrique). Pour des teneurs en silice de la présente invention (entre 10 et 60%), les proportions des Al_IV tétraédriques sont proches et s'établissent autour de 20 à 40%, et de manière préférée entre 24 et 31 %.
• L'environnement du silicium des silice-alumines étudié par la RMN de ²⁹Si montrent les déplacements chimiques des différentes d'espèces de silicium telles que Q⁴ (-105ppm à - 120 ppm), Q³ (-90ppm à -102 ppm) et Q² (-75ppm à - 93 ppm). Les sites avec un déplacement chimique à -102 ppm peuvent être des sites de type Q³ ou Q⁴, nous les appelons dans ce travail sites Q^3-4. Les silice-alumines de l'invention sont composées de silicium de types Q², Q³, Q^3-4 et Q⁴. De nombreuses espèces seraient de type Q², approximativement de l'ordre de 30 à 50 %. La proportion des espèces Q³ est également importante, approximativement de l'ordre de 10 à 30 %. Les définitions des sites sont les suivantes :
  • sites Q⁴ : Si lié à 4Si(ou Al)
  • sites Q³ : Si lié à 3 Si(ou Al) et 1 OH
  • sites Q² : Si lié à 2 Si(ou Al) et 2 OH;
• L'homogénéité des supports a été évaluée par Microscopie Electronique à Transmission. Nous cherchons par cette méthode à vérifier l'homogénéité de la répartition de Si et Al à l'échelle nanométrique. Les analyses sont réalisées sur des coupes ultra-fines des supports, par des sondes de taille différente, 50nm ou 15nm. Pour chaque solide étudié, 32 spectres sont enregistrés, dont 16 avec sonde de 50nm et 16 avec sonde à 15nm. Pour chaque spectre, des rapports atomiques Si/Al sont ensuite calculés, avec les moyennes des rapports, le rapport minimum, le rapport maximum et l'écart type de la série. La moyenne des rapports Si/Al mesurée par Microscopie Electronique à Transmission pour les différentes silice-alumines sont proches du rapport Si/Al obtenu par Fluorescence X. L'évaluation du critère homogénéité se fait sur la valeur de l'écart type.
  Suivant ces critères, un grand nombre de silice-alumines de la présente invention peuvent être considérées comme hétérogènes car elles présentent des rapports atomiques Si/Al avec des écarts types de l'ordre de 30-40%.

The following measurements were also performed on the silica-alumina:

• The diffractograms of the silica-aluminas of the invention, obtained by X-ray diffraction, correspond to a mixture of silica and alumina with a certain evolution between gamma-alumina and silica as a function of the SiO ₂ content. some samples. In these silica-aluminas, a less crystalline alumina is observed with respect to the alumina alone.
• The ²⁷ Al NMR spectra of silica-aluminas show two distinct peak mass. Each massif can be broken down into at least two species. We observe a broad dominance of species whose maximum resonates at 10 ppm and which ranges between 10 and 60 ppm. The position of the maximum suggests that these species are essentially of type Al _VI (octahedral). On all the spectra we observe a second of type of species which resonates towards 80-110 ppm. These species correspond to the atoms of AI _IV (tetrahedral). For silica contents of the present invention (between 10 and 60%), the proportions of the tetrahedral Al _IV are close and are around 20 to 40%, and preferably between 24 and 31%.
• The silica-alumina silicon environment studied by the ²⁹ Si NMR shows the chemical shifts of the various silicon species such as Q ⁴ (-105 ppm to -120 ppm), Q ³ (-90 ppm to -102 ppm). and Q ² (-75ppm to -93 ppm). Sites with a chemical displacement at -102 ppm may be sites of type Q ³ or Q ^4, we call this work Q websites ^3-4. The silica-aluminas of the invention are composed of silicon of types Q ² , Q ³ , Q ^3-4 and Q ⁴ . Many species would be of type Q ² , approximately of the order of 30 to 50%. The proportion of Q ³ species is also important, approximately of the order of 10 to 30%. The definitions of the sites are as follows:
  • sites Q ⁴ : If linked to 4Si (or Al)
  • sites Q ³ : If linked to 3 Si (or Al) and 1 OH
  • sites Q ² : If linked to 2 Si (or Al) and 2 OH;
• The homogeneity of the supports was evaluated by Transmission Electron Microscopy. We seek by this method to verify the homogeneity of the distribution of Si and Al at the nanoscale. The analyzes are carried out on ultra-thin sections of the supports, by probes of different size, 50nm or 15nm. For each solid studied, 32 spectra are recorded, including 16 with a 50 nm probe and 16 with a 15 nm probe. For each spectrum, reports Atomic Si / Al are then calculated, with the averages of the ratios, the minimum ratio, the maximum ratio and the standard deviation of the series. The average Si / Al ratios measured by Transmission Electron Microscopy for the various silica-aluminas are close to the Si / Al ratio obtained by X-ray fluorescence. The evaluation of the homogeneity criterion is made on the value of the standard deviation.
  According to these criteria, a large number of silica-aluminas of the present invention can be considered as heterogeneous because they have Si / Al atomic ratios with standard deviations of the order of 30-40%.

The support may consist of pure silica-alumina or result from mixing with said silica-alumina a binder such as silica (SiO ₂ ), alumina (Al ₂ O ₃ ), clays, titanium oxide (TiO ₂ ), boron oxide (B ₂ O ₃ ) and zirconia (ZrO ₂ ) and any mixture of binders previously mentioned. The preferred binders are silica and alumina and even more preferably alumina in all these forms known to those skilled in the art, for example gamma-alumina. The weight content of binder in the catalyst support is between 0 and 40%, more particularly between 1 and 40% and even more preferably between 5% and 20%. As a result, the weight content of silica-alumina is 60 - 100%. However, the catalysts according to the invention whose support consists solely of silica-alumina without any binder are preferred.

The support may be prepared by shaping the silica-alumina in the presence or absence of binder by any technique known to those skilled in the art. The shaping can be carried out for example by extrusion, pelletizing, by the method of coagulation in drop (oil-drop), by rotating plate granulation or by any other method well known to those skilled in the art. At least one calcination may be carried out after any of the steps of the preparation, it is usually carried out under air at a temperature of at least 150 ° C, preferably at least 300 ° C.

Finally, in a fourth preferred embodiment of the invention, the catalyst is a bifunctional catalyst in which a noble metal is supported by a support consisting essentially of an amorphous silica-alumina gel and micro / mesoporous membrane with a controlled pore size, having an area of at least 500 m ² / g and an SiO ₂ / Al ₂ O ₃ molar ratio of between 30/1 and 500/1, preferably between 40/1 and 150/1.

The noble metal supported on the support may be chosen from metals of Groups 8, 9 and 10 of the Periodic Table, in particular Co, Ni, Pd and Pt. Palladium and platinum are preferably used. The proportion of noble metals is normally between 0.05 and 5.0% by weight relative to the weight of the support. Particularly advantageous results have been obtained using palladium and platinum in proportions of between 0.2 and 1.0% by weight.

Said support is generally obtained from a mixture of tetra-alkylated ammonium hydroxide, an aluminum compound which can be hydrolysed to Al ₂ O ₃ of a silicon compound which can be hydrolyzed to SiO ₂ and a sufficient amount of water to dissolve and hydrolyze these compounds, said tetra-alkylated ammonium hydroxide having 2 to 6 carbon atoms in each alkyl residue, said hydrolyzable aluminum compound being preferably a trialkoxide of aluminum having 2 to 4 carbon atoms in each alkoxide residue and said hydrolysable silicon compound being a tetraalkylorthosilicate having 1 to 5 carbon atoms for each alkyl residue.

There are various methods for obtaining different media having the characteristics mentioned above, for example according to the descriptions presented in the European patent applications EP-A 340,868 , EP-A 659,478 and EP-A 812,804 . In particular, an aqueous solution of the compounds mentioned above is hydrolysed and gelled by heating it, either in a confined atmosphere to bring it to the boiling point or to a higher value, or in the open air, below this temperature. The gel thus obtained is then dried and calcined.

The tetra-alkylated ammonium hydroxide which may be used in the context of the present invention is, for example, chosen from hydroxides of tetraethylammonium, propylammonium, isopropylammonium, butylammonium, isobutylammonium, terbutylammonium and pentylammonium, and preferably from the hydroxides of tetrapropylammonium, tetraisopropylammonium and tetrabutylammonium. Trialkoxide aluminum is for example chosen from triethoxide, propoxide, isopropoxide, butoxide, isobutoxide and aluminum tertbutoxide, preferably from tripropoxide and tri-isopropoxide of aluminum. The tetra-alkylated orthosilicate is chosen, for example, from tetramethyl-, tetraethyl-, propyl-, isopropyl-, butyl-, isobutyl-, terbutyl- and pentyl-orthosilicate, tetraethylorthosilicate being used preferably.

According to a typical procedure for the preparation of the carrier, an aqueous solution containing tetra-alkylated ammonium hydroxide and aluminum trialkoxide is first prepared at a temperature sufficient to ensure effective dissolution of the aluminum compound. The tetra-alkylated orthosilicate is added to said aqueous solution. This mixture is brought to a temperature suitable for the activation of the hydrolysis reaction. This temperature depends on the composition of the reaction mixture (generally 70 to 100 ° C). The hydrolysis reaction is exothermic, which guarantees a self-sustaining reaction after activation. In addition, the proportions of the constituents of the mixture are such that they respect the following molar ratios: SiO ₂ / Al ₂ O ₃ of 30/1 to 500/1, tetra-alkylated ammonium hydroxide / SiO ₂ of 0.05 / 1 to 0.2 / 1, and H ₂ O / SiO ₂ from 5/1 to 40/1. The preferred values for these molar ratios are as follows: SiO ₂ / Al ₂ O ₃ from 40/1 to 150/1, tetra-alkylated ammonium hydroxide / SiO ₂ from 0.05 / 1 to 0.2 / 1, and H ₂ O / SiO ₂ from 10/1 to 25/1.

The hydrolysis of the reagents and their gelling are carried out at a temperature equal to or higher than the boiling point, at atmospheric pressure, of any alcohol developed as a by-product of said hydrolysis reaction, without any significant elimination or elimination. of these alcohols of the reaction medium. The hydrolysis and gelling temperature is therefore critical and is suitably maintained at values above about 65 ° C, of the order of about 110 ° C. In addition, in order to maintain the development of the alcohol in the reaction medium, it is possible to operate in an autoclave at the autogenous pressure of the system at the preselected temperature (normally of the order of 0.11-0.15 MPa abs.), Or at atmospheric pressure in a reactor equipped with a reflux condenser.

According to a particular embodiment of the process, the hydrolysis and gelling are carried out in the presence of an amount of alcohol greater than that developed as a by-product. For this purpose, a free alcohol, preferably ethanol, is added to the reaction mixture in a proportion up to a maximum molar ratio of added alcohol / SiO ₂ of 8/1.

The time required to carry out the hydrolysis and gelling under the conditions indicated above is normally between 10 minutes and 3 hours, preferably between 1 and 2 hours.

It has further been found that it may be useful to subject the gel thus obtained to aging by maintaining the reaction mixture in the presence of alcohol and under environmental temperature conditions for a period of about 1 to 24 hours.

The alcohol is finally extracted from the gel which is then dried, preferably under a reduced pressure (from 3 to 6 kPa for example), at a temperature of 110 ° C. The dried gel is then subjected to a calcination process under an oxidizing atmosphere (normally in air), at a temperature between 500 and 700 ° C for 4 to 20 hours, preferably at 500-600 ° C for 6 to 10 hours.

The silica gel and alumina thus obtained has a composition which corresponds to that of the reagents used, if it is considered that the reaction yields are practically complete. The molar ratio SiO ₂ / Al ₂ O ₃ is therefore between 30/1 and 500/1, preferably between 40/1 and 150/1, the preferred values being of the order of 100/1. This gel is amorphous, when subjected to X-ray powder diffraction analysis, it has an area of at least 500 m ² / g, generally between 600 and 850 m ² / g, and a pore volume of 0.4 to 0.8 cm ³ / g _.

A metal selected from the noble metals of groups 8, 9 or 10 of the periodic table is supported on the micro / mesoporous amorphous silica-alumina gel obtained as described above. As indicated above, this metal is preferably chosen from platinum or palladium, platinum being preferably used.

The proportion of noble metal, especially platinum, in the catalyst thus supported is between 0.4 and 0.8%, preferably between 0.6 and 0.8% by weight relative to the weight of the support.

It is advantageous to distribute the metal evenly over the porous surface of the support to maximize the effective catalytic surface. Various methods can be implemented for this purpose, such as those described, for example, in the European patent application. EP-A 582,347 whose contents are mentioned here for reference. In particular, according to the impregnation technique, the porous support having the characteristics of the acid carrier (a) described above is brought into contact with an aqueous or alcohol solution of a compound of the desired metal for a time sufficient to allow a homogeneous distribution of the metal in the solid. This operation normally requires a few minutes to several hours, preferably with stirring. H ₂ PtF ₆ , H ₂ PtCl ₆ , [Pt (NH ₃ ) 4] Cl ₂ , [Pt (NH ₃ ) ₄ ] (OH) ₂ are, for example, soluble salts suitable for this purpose, as well as salts of palladium; mixtures of salts of different metals are also used in the context of the invention. It is advantageous to use the minimum amount of aqueous liquid (usually water or an aqueous mixture with a second inert liquid or with an acid in a proportion of less than 50% by weight) necessary for dissolving the salt and impregnating uniformly said support, preferably with a solution / support ratio of between 1 and 3. The amount of metal used is chosen according to the desired concentration in the catalyst, the entire metal being fixed on the support.

At the end of the impregnation, the solution is evaporated and the solid obtained is dried and calcined under an inert or reducing atmosphere, under conditions of temperature and time similar to those previously described for the calcination of the support.

Another method of impregnation is by means of an ion exchange. For this purpose, the support consisting of amorphous silica-alumina gel is brought into contact with an aqueous solution of a salt of the metal used, as in the previous case, but the deposition is carried out by ion exchange, under conditions made basic (pH between 8.5 and 11) by the addition of a sufficient amount of an alkaline compound, usually an ammonium hydroxide. The suspended solid is then separated from the liquid by filtration or decantation, and then dried and calcined as described above.

According to yet another method, the salt of the transition metal may be included in the silica-alumina gel during the preparation phase, for example before hydrolysis for the formation of the wet gel, or before its calcination. Although the latter method is advantageously easier to implement, the catalyst thus obtained is slightly less active and selective than that obtained with the two previous methods.

The supported catalyst described above can be used as it is during the hydrocracking step of the process according to the present invention, after activation according to one of the known methods and / or described below. However, according to a preferred embodiment, said supported catalyst is reinforced by the addition with mixing of a suitable amount of an inert mineral solid capable of improving its mechanical properties. In fact, the catalyst is preferably used in granular form rather than in powder form with a relatively tight particle distribution. In addition, it is advantageous for the catalyst to have sufficient compressive and impact strength to prevent progressive crushing during the hydrocracking step.

Extrusion and shaping methods are also known which use a suitable inert additive (or binder) capable of providing the properties mentioned above, for example according to the methods described in the European patent applications. EP-A 550,922 and EP-A 665.055 , the latter being preferably implemented, their contents being mentioned here by way of reference.

1. (a) la solution de composants hydrolysables obtenue comme décrit ci-avant est chauffée pour provoquer l'hydrolyse et la gélification de ladite solution et pour obtenir un mélange A présentant une viscosité comprise entre 0,01 et 100 Pa.sec ;
2. (b) un liant appartenant au groupe des bohémites ou des pseudobohémites est d'abord ajouté au mélange A, dans un rapport pondéral avec le mélange A compris entre 0,05 et 0,5, puis un acide minéral ou organique est ajouté dans une proportion comprise entre 0,5 et 8,0 g pour 100 g de liant ;
3. (c) le mélange obtenu en (b) est porté sous agitation à une température comprise entre 40° et 90°C jusqu'à obtention d'une pâte homogène qui est ensuite soumise à une étape d'extrusion et de granulation ;
4. (d) le produit extrudé est séché et calciné sous atmosphère oxydante.

A typical method of preparing the catalyst in extruded form ( EP-A 665.055 ) has the following steps:

1. (a) the solution of hydrolysable components obtained as described above is heated to cause the hydrolysis and gelling of said solution and to obtain a mixture A having a viscosity of between 0.01 and 100 Pa.sec;
2. (b) a binder belonging to the group of bohemites or pseudobohemites is first added to the mixture A, in a weight ratio with the mixture A of between 0.05 and 0.5, and then a mineral or organic acid is added in a proportion of between 0.5 and 8.0 g per 100 g of binder;
3. (c) the mixture obtained in (b) is stirred at a temperature of between 40 ° and 90 ° C until a homogeneous paste is obtained which is then subjected to an extrusion and granulation step;
4. (d) the extruded product is dried and calcined under an oxidizing atmosphere.

Plasticizers such as methylcellulose are also preferably added during step (b) to promote the formation of a homogeneous, easily treated mixture.

A granular acidic support comprising from 30 to 70% by weight of inert inorganic binder is thus obtained, the remaining proportion consisting of amorphous silica-alumina having essentially the same characteristics of porosity, surface and structure as those described above for the same gel without binder. The granules are advantageously in the form of pellets approximately 2-5 mm in diameter and 2-10 mm long.

The deposition step of the noble metal on the granular acidic support is then carried out according to the same procedure as that described above.

After the preparations (e.g. those described in the above embodiments) and before use in the conversion reaction, the metal contained in the catalyst must be reduced. One of the preferred methods for conducting the reduction of the metal is hydrogen treatment at a temperature of from 150 ° C to 650 ° C and a total pressure of 0.1 to 25 MPa. For example, a reduction consists of a stage at 150 ° C. for 2 hours then a rise in temperature up to 450 ° C. at the rate of 1 ° C./min and then a plateau of 2 hours at 450 ° C. throughout this reduction step, the hydrogen flow rate is 1000 l hydrogen / catalyst. Note that any in situ or ex-situ reduction method is suitable.

1. 1) 2 heures à température ambiante sous un courant d'azote ;
2. 2) 2 heures à 50°C sous un courant d'hydrogène ;
3. 3) chauffage à 310-360°C avec une vitesse d'élévation de la température de 3°C/min sous un courant d'hydrogène ;
4. 4) température constante à 310-360°C pendant 3 heures sous un courant d'hydrogène et refroidissement à 200°C.

Preferably and in particular for the catalyst of the last preferred embodiment a typical method implements the procedure described below:

1. 1) 2 hours at room temperature under a stream of nitrogen;
2. 2) 2 hours at 50 ° C under a stream of hydrogen;
3. 3) heating at 310-360 ° C with a rate of temperature rise of 3 ° C / min under a stream of hydrogen;
4. 4) constant temperature at 310-360 ° C for 3 hours under a stream of hydrogen and cooling at 200 ° C.

During activation, the pressure in the reactor is maintained between 30 and 80 atm.

Claims (8)

1. A process for producing middle distillates from a paraffin effluent produced by Fischer-Tropsch synthesis, comprising the following successive steps:

   a) optionally, fractionating the feed into at least one heavy fraction with an initial boiling point in the range 120-200°C, and at least one light fraction boiling below said heavy fraction;

   b) optionally, hydrotreating at least a portion of the effluent or the heavy fraction, optionally followed (step c) by eliminating at least a portion of the water;

   d) passing at least a portion of the effluent or of the optionally hydrotreated fraction over a first hydroisomerisation/hydrocracking catalyst, which is an amorphous catalyst containing at least one noble group VIII metal;

   a) distilling the hydroisomerised/hydrocracked effluent to obtain middle distillates (kerosine, gas oil) and a residual fraction boiling above the middle distillates;

   b) passing at least a portion of said residual heavy fraction and/or a portion of said middle distillates over a second hydroisomerisation/hydrocracking catalyst, which is an amorphous catalyst containing at least one noble group VIII metal, and distilling the resulting effluent to obtain middle distillates.
2. A process according to claim 1, in which a portion of at least one of the kerosine, gas oil cuts from step e) is recycled to step d) and the residual fraction undergoes step f).
3. A process according to claim 1, in which at least one of the kerosine, gas oil cuts from step e) undergoes step f), and the residual fraction is recycled to step d).
4. A process according to any one of the preceding claims, in which the process includes step a) and the light fraction separated in step a) is sent to a steam cracking step.
5. A process according to any one of the preceding claims, in which the hydroisomerisation/hydrocracking catalysts contain no added halogen.
6. A process according to any one of the preceding claims, in which for the first catalyst, the conversion is less than 50% by weight for converting products with boiling points of 150°C or more to products with boiling points of less than 150°C.
7. A process according to any one of the preceding claims, in which, for the second catalyst, the residual fraction is treated with a conversion of more than 40% by weight, for converting products with a boiling point of 370°C or more to products with a boiling point of less than 370°C.
8. A process according to any one of the preceding claims, in which, for the second catalyst, a portion of the kerosine and/or gas oil is treated with a conversion of less than 50% by weight, for converting products with a boiling point of 150°C or more to products with a boiling point of less than 150°C.

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