WO2007006924A1

WO2007006924A1 - Use of a catalyst for opening hydrocarbon rings

Info

Publication number: WO2007006924A1
Application number: PCT/FR2006/001616
Authority: WO
Inventors: Sébastien LECARPENTIER; Jacob Van Gestel; Jean-Pierre Dath; Christine Collet; Jean-Pierre Gilson
Original assignee: Total France; Centre National De La Recherche Scientifique
Priority date: 2005-07-08
Filing date: 2006-07-06
Publication date: 2007-01-18
Also published as: FR2888131B1; FR2888131A1; WO2007006924A8; EP1919612A1

Abstract

The invention relates to the use of a solid catalyst for opening hydrocarbon rings, which is comprised of: a mesoporous zirconium oxide (ZrO2) support, optionally doped with silica; tungsten oxide (WO3) in a quantity such that the mean number of tungsten (W) atoms by nm2 of specific area of zirconium oxide (ZrO2) ranges between 0.1 to 9, and; 0.1 to 5 %, with regard to the total weight of the solid catalyst, iridium. The invention also relates to a method for opening the ring of cyclic hydrocarbon compounds by using a catalytic composition of the aforementioned type.

Description

Use of a catalyst for opening hydrocarbon rings

The present invention relates to a use as a ring-opening catalyst of a catalytic composition based on zirconia, tungsten oxide and metallic iridium, and a process for catalytic ring opening of hydrocarbon feedstocks comprising the use of this composition, to open the cycles of naphthenic compounds present in hydrocarbon feeds.

The conversion of the light cycle oil (LCO) fraction from fluidized bed catalytic cracking (FCC) to diesel fuel meeting the most stringent environmental standards requires extensive desulphurization and denitrogenation and hydrogenation of polycyclic aromatic hydrocarbons (PAHs). followed by a ring opening reaction of the naphthenic molecules formed. This ring opening reaction can lead either to the formation of smaller hydrocarbons or to the cleavage of a single C-C bond of the naphthenic ring without reducing the number of carbon atoms. This opening of naphthenic rings without cracking is particularly advantageous because the weakly branched alkanes formed increase the cetane number of the treated feedstock and reduce its density. The ring opening catalysts are conventionally metals of group VIII of the periodic table of elements such as Pt, Ru, Ir and Rh, immobilized on a silica, alumina or alumino-silicate support.

It is further known that the hydrogenolysis of C 8 hydrocarbon rings is more convenient than the opening of C 6 rings and several publications describe the use, in addition to the metal catalyzing the dirhydrogenolysis reaction, of a "ring contraction" metal. Which introduces a limited number of acidic sites promoting isomerization of C6 rings in Cs rings (Journal of Catalysis, 210, 137-148, 2002, US 5,763,731). The metals favoring the contraction of the cycles are generally chosen from those of the group

VIA, and the preferred metal is tungsten.

Thus, US Pat. No. 6,235,962 discloses a catalytic composition for the ring opening of cyclic organic compounds, comprising from 0.1 to 10% by weight of a catalytically active metal chosen from platinum, palladium, rhodium and rhenium, iridium, ruthenium, nickel, cobalt, associated with 0.01 to 20% by weight of a modifying agent selected from tungsten, molybdenum, lanthanum and rare earth metals, these metals being immobilized on inorganic supports selected from alumina, silica, zirconia and mixtures thereof. Almost all the examples of this patent relate to catalytic supports based on alumina.

In the context of its research aimed at optimizing the yields and the selectivity of naphthenic ring opening processes, the Applicant has found that the use of a mesoporous zirconia as a catalytic support allows an excellent control of the number of acidic sites. , responsible for the isomerization of C6 rings in Cs rings, by introduction into the support, of tungsten atoms in the form of oxyanions. The control of the acidity by introducing tungsten into a zirconia support is much more accurate than for known supports of the alumina, silica or aluminosilicate type. Moreover, the tungsten contents necessary for obtaining a given Cβ → Cs isomerization activity are lower on a zirconia support than on the known alumina, silica or aluminosilicate substrates.

The use of a support based on tungsten-associated mesoporous zirconia, in the form of oxyanions, has made it possible to carry out systematic studies for the determination of the optimum quantities of iridium, a very interesting hydrogenation metal, but a very high cost. The Applicant has thus found that the best results of ring opening (in terms of conversion and selectivity) are obtained for relatively low levels of iridium, generally less than 2% relative to the total weight of the catalyst. and for tungsten contents lower or similar to those required for the formation of a monolayer of tungsten oxide. The subject of the present invention is therefore a use as catalyst for opening hydrocarbon-based rings of a catalytic composition comprising particles of a solid catalyst, consisting of

(a) a mesoporous zirconia (ZrO 2) support, optionally doped with silica, having a specific surface area between

90 and 300 m ² / g, preferably between 120 and 250 m ² / g, (b) tungsten oxide (WO 3) in an amount such that the average number of tungsten atoms (W) per nm ² of zirconia specific surface (ZrO 2) is between 0, 1 and 9, and

(c) from 0.1% to 5%, based on the total weight of the solid catalyst, of iridium.

The zirconia (ZrO 2) used as a support for the catalyst of the present invention is generally a mesoporous zirconia having an average pore size of between 2 and 50 nm. This relatively larger pore size than the zeolite supports described in the state of the art facilitates the transport of reagents and products. The specific surface area of the zirconia is preferably between 90 and 300 m ² / g and in particular between 90 and 250 m ² / g.

It is known to stabilize the zirconia and to increase its specific surface area by doping it with small amounts of silica. The introduction of silica into catalytic supports based on zirconia is described in patent application EP 1 053 785. In this application, the zirconia is doped by adding silica particles to a suspension of zirconia particles, ripening of the suspension, filtration and calcination. The porous zirconia doped with silica thus obtained have a crystalline structure and specific surfaces greater than 160 m ² / g. The weight ratio of zirconia (zirconium dioxide) to silica (silicon dioxide) of the doped zirconia described in EP 1 053 785 and usable in the present invention is between 5 and 70.

Zirconia can also be doped with silica by coprecipitation of zirconia and silica, for example from suitable chlorinated precursors such as ZrOCb and SiCl ₄ . In this variant of the preparation process, the precipitate formed must also be subjected to a heat-curing step, for example heating at 80 ^° C. to 95 ^° C. for 1 to 2 days, followed by a maturing step of several days (2 - 5 days) at room temperature.

The introduction of acid sites by modification of the zirconia with metatungstate ions can be done for example by impregnation of the zirconia, doped or undoped with silica, with a solution of (NH4) 6H2Wi2θ40, 8H2O, evaporation of the phase aqueous, drying, then calcination (for example 3 hours at 750 ⁰ C). The calcination results in the formation of a mesoporous crystalline product based on ZrO 2, optionally doped with SiO ₂ and supporting metatungstate ions. In the remainder of the description, the term "zirconia" encompasses both undoped zirconia and zirconia doped with silica.

In the context of the study aimed at optimizing the catalytic properties of the ring-opening catalysts of the present invention, the Applicant has found that the activity of the catalyst, and in particular the degree of conversion and the selectivity of the reaction, depended on the amount of tungsten introduced into the catalytic support. This amount of tungsten can be expressed either as a number of tungsten atoms per unit area of zirconia (nm ² ) or as a percentage by weight. The Applicant has chosen to define the catalysts used according to the present invention by the number of W atoms per nm ² of zirconia surface, since this quantity better reflects the configuration of the catalyst surface. The indication of the percentage by weight of tungsten does not take into account the specific surface of the support and does not inform about the superficial concentration of tungsten. Thus, the same percentage by weight of tungsten could correspond as well to a partial coverage of the surface (for a high specific surface support) as to a superposition of several layers of tungsten (for a low specific surface support).

The method for calculating the number of W atoms from the value of the specific surface, determined by nitrogen adsorption according to the BET method, and the tungsten content of the modified support, determined by atomic absorption, is explained in FIG. detail in example 1 below.

The catalysts used according to the present invention preferably have an average number of tungsten atoms (W) per nm ² of zirconia specific surface area (ZrO 2) between 0.5 and 5, more preferably between 1 and 3 and in particular between 1,2 and 2. These values correspond to a partial coverage of the zirconia surface, ie to a quantity of tungsten lower or similar to that necessary to form a monolayer of WO3. The number of tungsten atoms necessary for the formation of a monolayer of WO 3 is indeed estimated between 4 and 7 W / nm ² atoms in the literature (J. Phys Chem B 103.7206-7213, 1999 J. Cotai,

225, 45 - 55, 2004; J. Catal, 231, 468-479, 2005; J. Phys. Chem., 103, 630 - 640, 1999) The number of tungsten atoms per unit area of support, however, is not the only parameter governing the catalytic activity of the catalyst used according to the invention. The second determining parameter is the content of iridium, a metal that catalyzes the lysis of hydrogenolysis, that is to say, the breaking of the cycle without decreasing the molecular weight. This content is preferably between 0.15 and 3%, in particular between 0.2 and 2% and more preferably between 0.3 and 1.5%, relative to the total weight of the solid catalyst.

In a particularly preferred embodiment of the invention, the tungsten surface concentration is combined with the optimum content of iridium, that is, the amount of tungsten oxide (WO 3) is such that the average number of tungsten atoms (W) per nm ² of zirconia specific surface (ZrO 2) is between 1.2 and 2, and the amount of iridium is between 0.3 and 1.5%, based on the total weight of the solid catalyst. The catalysts exhibiting these levels of tungsten and iridium have made it possible to obtain ring opening selectivities by hydrogenolysis of 80% to 90% for methylcyclohexane conversion ratios (model compound used for the comparative evaluation of cycle) of the order of 50% to 90%.

The catalyst particles can of course be incorporated in known manner in a binder and / or an inert matrix, for example based on silica, alumina or aluminophosphates, allowing, for example, the production of extrudates ready to be introduced into the reactors.

The present invention also relates to a process for the catalytic ring opening of hydrocarbon feedstocks, comprising the use of a catalytic composition as defined above with a hydrocarbon feed containing mono- or polycyclic compounds, aromatic or naphthenic, under pressure. of hydrogen ranging between 1 and 120 bar, preferably between 2 and 60 bar, at a temperature between 200 ⁰ C and 450 ° C, preferably between 250 and 350 ⁰ C, and with a space velocity of between 0, 1 and 10 h ^-1 , preferably between 1 and 5 h ^-1 . Example 1

Determination of the number of tungsten atoms per unit area of zirconia from the catalyst analysis results

To calculate the number of tungsten atoms per unit area of zirconia, one needs (a) the weight percentage of tungsten of the catalyst after calcination (before impregnation of iridium) determined by atomic absorption and (b) the surface specific (in m ² / g) of the product obtained after calcination, determined according to the BET method. For low tungsten contents, the specific surface area experimentally measured on the product containing both zirconia and tungsten oxide can be compared to the specific surface area of zirconia alone, and the number of W atoms per nm ² of zirconia surface D ₁ can be calculated according to the following formula:

% P x N _A ⁽¹⁾ '^" 183.84 x S ₁ x 10 ¹⁸ where

% P is the tungsten weight fraction of the product, determined by atomic absorption,

NA is the number of Avogadro (6,023.10 ²³ atoms / mole), 183,84 is the atomic weight of tungsten,

S ₁ is the specific surface determined experimentally by the BET method and expressed in m ² / g.

When the tungsten contents of the calcined product (ZrO 2 + WO 3) are high (> 10% by weight), it is necessary to calculate, before using the formula above, a corrected specific surface area. In fact, the specific surface area determined experimentally is the area per gram of mixture of ZrO 2 and WO 3, and it is assumed that the surface of the catalyst is due solely to the ZrO 2 support. To express the specific surface area with respect to the zirconia, it is therefore necessary to subtract the weight of the ZrO 2 and WO 3 mixture from the weight of the tungsten oxide. The corrected area S ₁ 'will be calculated as follows:

OR

% P and S ₁ have the meaning indicated above,

(183,48 + 48) is the atomic mass of tungsten trioxide

For the calculation of the number of tungsten atoms per nm ² of zirconia, then, in equation 1 above, the value of the measured specific surface area S ₁ is replaced by that of the corrected specific surface area Si.

From the number of tungsten atoms per nm ² of zirconia, one can of course find the weight fraction of tungsten (% P) in the catalyst (ZrO 2 + WO 3) by using the following formula:

where D ₁ is the value of the average number of tungsten atoms per nm ² of zirconia surface,

S ₁ is the specific surface area experimentally measured by nitrogen adsorption (BET),

NA is the number of Avogadro

Calculating% P then involves solving the following second-degree equation:

1, 26 X ² - X + D ₁ S ₁ 3.052.10- ⁴ = 0 where X =% P

Example 2

Preparation of a ring opening catalyst used according to the invention

To an aqueous solution of ZrOCb octahydrate (0.207 mol / L) and SiCl ₄ (1.26 × 10 ^-2 mol / L) is added dropwise NH ₄ OH (10 mol / L) to pH 9 A precipitate is formed and the suspension thus obtained is heated under slight reflux without stirring for 2 days at a temperature of 90 ^° C. (heat-curing stage), and then for 4 days at room temperature at rest (curing stage at room temperature). cold). After filtration, several washes to remove Cl and drying at 120 ° C, a powder containing 1, 2% by weight of Si is obtained.

16 g of the powder obtained are suspended in 50 ml of an aqueous solution of (NH ₄ ) OH ₂ Wi ₂ O ₄ O ₈ H ₂ O at 6.64 × 10 ^-4 mol / l. 55 ° C. at atmospheric pressure, then dried at 120 ^° C. The powder obtained is then subjected to calcination for 3 hours at 750 ^° C. The calcined product is a white crystalline powder The specific surface (91 m ² / g ) and the tungsten content (4.28% by weight) are determined on a sample of these crystals.Using the calculation method of Example 1, a number of tungsten atoms per nm ² of equal zirconia is obtained. at 1, 5.

The remainder of the crystals is impregnated with a volume slightly greater than the pore volume (pore volume plus approximately 10%) of a solution of IrCb containing the desired quantity of iridium, dried at 120 ^° C. and then a second calcination is carried out for 3 hours to

450 ⁰ C, under a stream of air. The deposited iridium is then reduced by a reduction step at 350 ^° C. under a flow of H ₂ .

The iridium content of the catalyst thus obtained is equal to 1, 2% by weight.

Example 3

Method of decycling methylcyclohexane using a catalyst used according to the invention

Three series of ring-opening reactions of a model molecule, methylcyclohexane, are carried out in a plug-flow reactor using two catalysts used according to the invention and a comparative ring opening catalyst containing the same percentage of catalyst. iridium but which is free of tungsten.

Figure 1 shows the results of these ring-opening reactions in terms of aperture selectivity as a function of the conversion rate of methylcyclohexane. By "open selectivity" is meant the ratio by weight of the linear and branched Cγ compounds produced to the sum of the cracking products, the linear and branched Cγ compounds produced and isomerization products without ring opening.

The conversion of methylcyclohexane can be increased indifferently either by a rise in the reaction temperature (between 250 and 325 ⁰ C for Figure 1) or by an extension of the contact time, in other words by a reduction in the hourly space velocity of the methylcyclohexane stream (between 5 and 10 h ^-1 for Figure 1). The catalysts used according to the invention for the preparation of FIG. 1 have an iridium content equal to 1.2% by weight and a number of tungsten atoms per nm ² of zirconia surface of 1.7 (empty squares, D) and 1.5 (solid squares, m) The comparative catalyst (solid triangles, λ) contains 1.2% by weight of iridium and 0% of tungsten, and Figure 1 shows that the catalysts used according to US Pat. The invention makes it possible to obtain a high opening selectivity of the order of 80 to 90%, especially for high methylcyclohexane conversions, whereas the tungsten-free catalyst gives satisfactory selectivity values only for very low methylcyclohexane conversions. , cracking reactions becoming pre weighting for higher conversion rates.

Example 4

Process for converting decalin using a catalyst used according to the invention

Three series of ring-opening reactions of a model molecule, decalin, are carried out in a piston-flow reactor using a catalyst used according to the invention, with an iridium content equal to 1.2% by weight and of number of tungsten atoms per nm ² of zirconia area of 1.5.

Activation is produced according to the following conditions:

Calcination under air at 400 ^° C. for 2 hours (ramp 3 ° / min);

Reduction in hydrogen at 35O ⁰ C for 1 hour (ramp 37min); and

Pressurizing (50 bars, where 1 Bar = 10 ⁵ Pa).

The reaction is carried out according to the following conditions:

• decalin - heptane mixture: 11-89% vol; • decalin pressure 0, 12 bar;

• contact time: 400 g. h / mol decalin; and

• temperature: 200 - 325 ⁰ C. Contraction is understood to mean: ClO contraction products / initial amount of ClO, by 1 open cycle: products of 1 ClO open cycle / initial amount of ClO, by cracking: ClO cracking products / initial amount of ClO, by conversion of ClO: (initial quantity of C10 - C10 remaining) / initial amount of ClO, and ClO cracking products: total cracking - initial amount of C7.

The results are given in the following two tables:

yield

T ( ⁰ C) Contraction Contraction Opening Cycle decalin cracking of a cycle

%%%%

200 0.58 0.58 0.00 0.00

225 4.84 2.93 0.00 1, 91

250 19.42 13.57 1, 93 3.92

275 46.27 29.74 9.36 7.17

300 80.15 30.93 16.43 32.79

325 91, 84 20.51 14.84 56.49

selectivity

T ( ⁰ C) Conversion Contraction Opening Decalin cracking

%%%%

200 0.58 100.00 0.00 0.00

225 4.84 60.60 0.00 39.40

250 19.42 69.87 9.95 20.18

275 46.27 64.28 20.23 15.49

300 80.15 38.60 20.50 40.90

325 91, 84 22.33 16.15 61, 51

It is therefore found that the catalyst used according to the invention makes it possible to obtain a moderate open selectivity, approximately 20%, for a low conversion, of the order of 15 to 30%, of decalin.

Claims

1. Use as catalyst for opening hydrocarbon-based rings of a catalytic composition comprising particles of a solid catalyst consisting of (a) a mesoporous zirconia support (ZrO 2), optionally doped with silica, having a specific surface area between 90 and 300 m ² / g, preferably between 120 and 250 m ² / g,

(b) tungsten oxide (WO 3) in an amount such that the average number of tungsten atoms (W) per nm ² of zirconia specific surface (ZrO 2) is between 0, 1 and 9, and

2. Use according to claim 1, characterized in that the amount of tungsten oxide (WO3) is such that the average number of tungsten atoms (W) per nm ² of specific surface of zirconia

(ZrO 2) is between 0.5 and 5, preferably between 1 and 3 and more preferably between 1, 2 and 2.

3. Use according to one of claims 1 or 2, characterized in that the amount of iridium is between 0, 15 and 3%, preferably between 0.2 and 2% and more preferably between 0.3 and 1.5%, based on the total weight of the solid catalyst.

4. Use according to one of claims 2 or 3, characterized in that the amount of tungsten oxide (WO3) is such that the average number of tungsten atoms (W) per nm ² of specific surface zirconia (ZrO 2) is between 1, 2 and 2, and the amount of iridium is between 0.3 and 1.5%, based on the total weight of the solid catalyst.

5. Process for catalytic ring opening of hydrocarbon feeds, comprising the use of a catalytic composition according to any one of the preceding claims with a hydrocarbon feed containing mono- or polycyclic compounds, aromatic or naphthenic, under a hydrogen pressure of between 1 and 120 bar, at a temperature between 200 ⁰ C and 450 ⁰ C, and with a space velocity of between 0.1 and 10 rr ¹ .