EP1369466B1 - Hydrodesulfurization of sulphur and olefins containing fractions with a metals of groups VIII and VIB containing supported catalyst. - Google Patents

Description

The present invention relates to a catalyst comprising at least one support, at least one group VIB element and at least one group VIII element and allowing the hydrodesulfurization of hydrocarbon feedstocks, preferably of the catalytic cracking gasoline (FCC) type. or catalytic cracking in a fluidized bed).
The invention more particularly relates to a process for the hydrodesulfurization of gasoline cuts in the presence of a catalyst comprising at least one element of group VIII, at least one element of group VIB, and a specific surface support of less than 200 m ² / g , wherein the density of Group VIB elements per unit area of the support is between 4.10 ^-4 and 36.10 ^-4 g of Group VIB element oxides per m ² of support.

PRIOR ART

The gasoline cuts and more particularly the gasolines from the FCC contain about 20 to 40% of olefinic compounds, 30 to 60% of aromatics and 20 to 50% of saturated paraffins or naphthenes type compounds. Of the olefinic compounds, the branched olefins are in the majority with respect to linear and cyclic olefins. These gasolines also contain traces of highly unsaturated diolefinic compounds which can deactivate the catalysts by forming gums. Thus, the patent EP 685 552 B1 proposes to selectively hydrogenate the diolefins, that is to say without transforming the olefins, before carrying out the hydrotreatment for the removal of sulfur. The content of sulfur compounds in these species varies widely depending on the type of gasoline (steam cracker, catalytic cracking, coking, etc.) or in the case of catalytic cracking of the severity applied to the process. It can fluctuate between 200 and 5000 ppm S, preferably between 500 and 2000 ppm with respect to the mass of filler. The families of thiophene and benzothiophene compounds are the majority, mercaptans being present at very low levels generally between 10 and 100 ppm. FCC gasolines also contain nitrogen compounds in proportions generally not exceeding 100 ppm.
In particular, the production of reformulated species that meet the new environmental standards requires that their olefin concentration be reduced as little as possible in order to maintain a high octane number, but that significantly decreases their sulfur content. Thus, current and future environmental standards require refiners to reduce the sulfur content in gasolines to values of 50 ppm or less in 2003 and 10 ppm beyond 2005. These standards concern the total sulfur but also the nature of sulfur compounds such as mercaptans. Catalytic cracking gasolines, which can represent 30 to 50% of the gasoline pool, have high olefin and sulfur contents. Sulfur in reformulated gasoline is almost 90% attributable to FCC gasoline. The desulphurisation (hydrodesulfurization) of gasolines and mainly FCC species is therefore of obvious importance for the respect of the specifications. The hydrotreating (or hydrodesulphurization) of catalytic cracking gasolines, when carried out under standard conditions known to those skilled in the art, makes it possible to reduce the sulfur content of the cut. However, this method has the major disadvantage of causing a very significant drop in the octane number of the cut, due to the saturation of all the olefins during the hydrotreatment. It has therefore been proposed methods for deep desulfurization of FCC gasolines while maintaining the octane number at a high level.

So, the U.S. Patent 5,318,690 proposes a process of splitting the gasoline, softening the light fraction and hydrotraying the heavy fraction on a conventional catalyst and then treating it on a zeolite ZSM5 to find approximately the initial octane number.
The request for WO 01/40409 claims the treatment of an FCC gasoline under conditions of high temperature, low pressure and high hydrogen / charge ratio. Under these particular conditions, the recombination reactions leading to mercaptan formation, involving the H ₂ S formed by the desulfurization reaction and the olefins are minimized.
Finally, U.S. Patent 5,968,346 proposes a scheme for achieving very low residual sulfur content by a multistage process: hydrodesulphurization on a first catalyst, separation of the liquid and gaseous fractions, and second hydrotreatment on a second catalyst. The liquid / gas separation makes it possible to eliminate the H ₂ S formed in the first reactor, in order to achieve a better compromise between hydrodesulfurization and octane loss.

Obtaining the desired reaction selectivity (ratio between hydrodesulfurization and hydrogenation of olefins) may therefore be partly due to the choice of the process, but in all cases the use of an inherently selective catalytic system is very often a key factor.

In general, the catalysts used for this type of application are sulphide catalysts containing a group VIB element (Cr, Mo, W) and a group VIII element (Fe, Ru, Os, Co, Rh , Ir, Pd, Ni, Pt). So in the US Patent 5,985,136 , it is claimed that a catalyst having a surface concentration of between 0.5 × 10 ^-4 and ₃ × ₁₀ ^-4 gMoO ₃ / m ² makes it possible to achieve high selectivities in hydrodesulfurization (93% hydrodesulfurization (HDS) against 33% hydrogenation of olefins (HDO)). Moreover, according to US Patents 4140626 and US 4,774,220 it may be advantageous to add a dopant (alkaline, alkaline earth) to the conventional sulphide phase (CoMoS) in order to limit the hydrogenation of the olefins.

Another way to improve the intrinsic selectivity of the catalysts is to benefit from the presence of carbonaceous deposits on the catalyst surface. So, the US Patent 4,149,965 proposes to pretreat a conventional naphtha hydrotreatment catalyst to partially deactivate it prior to its use for the hydrotreatment of gasolines. Similarly, the request for EP 0 745 660 A1 indicates that the pretreatment of a catalyst to deposit between 3 and 10% by weight of coke improves the catalytic performance. In this case, it is specified that the C / H ratio must not be greater than 0.7.

US Patent 6126814 describes a process for the hydrodesulfurization of naphtha in the presence of a catalyst containing MoO ₃ and CoO on a support.

SUMMARY OF THE INVENTION

In the present invention, it has been found a catalyst that can be used in a gasoline hydrodesulphurization process and that makes it possible to reduce the total sulfur and mercaptan content of the hydrocarbon cuts, and preferably of FCC gasoline cuts, without any significant loss of carbon dioxide. gasoline and minimizing the decrease in the octane number.

The invention more specifically relates to a process for the hydrodesulphurisation of gasoline cuts in the presence of a catalyst comprising at least one element of group VIII, at least one element of group VIB, and a support having a specific surface area of less than about 200 m ² / g, in which the density in Group VIB elements per unit area of the support is between 4.10 ^-4 and 36.10 ^-4 g of Group VIB element oxides per m ² of support.

DETAILED DESCRIPTION OF THE INVENTION

The charge to be hydrotreated (or hydrodesulphurized) by means of the process according to the invention is generally a petrol cut containing sulfur; such as for example a section resulting from a coking unit (coking according to the English terminology), visbreaking (visbreaking according to the English terminology), steam cracking (steam cracking according to the English terminology) or cracking catalytic (FCC, Fluid Catalytic Cracking according to the English terminology). Said filler preferably consists of a gasoline cut from a catalytic cracking unit whose boiling point range typically extends from the boiling points of hydrocarbons with 5 carbon atoms to 250 ° C. . This gasoline may optionally be composed of a significant fraction of gasoline from other production processes such as atmospheric distillation (gasoline derived from a straight-run distillation or straight-run gasoline according to the English terminology). conversion (coking or steam cracking gasoline).

The hydrodesulfurization catalysts according to the invention are catalysts comprising at least one element of group VIB and at least one element of group VIII on a suitable support. The element or elements of group VIB are preferably chosen from molybdenum and / or tungsten and the group VIII element or elements are preferably chosen from nickel and / or cobalt. The catalyst support is usually a porous solid selected from the group consisting of: aluminas, silica, silica alumina or even titanium or magnesium oxides used alone or in admixture with alumina or silica alumina. It is preferably selected from the group consisting of: silica, the family of transition aluminas and silica alumina, very preferably, the support consists essentially of less a transition alumina, that is to say it comprises at least 51% by weight, preferably at least 60% by weight, very preferably at least 80% by weight, or even at least 90% by weight of alumina of transition. It may optionally consist solely of a transition alumina.

The specific surface of the support according to the invention is generally less than 200 m ² / g, preferably less than 170 m ² / g and even more preferably less than 150 m ² / g, or even less than 135 m ² / g boy Wut. The carrier may be prepared using any precursor, method of preparation and any shaping tool known to those skilled in the art.

The catalyst according to the invention can be prepared using any technique known to those skilled in the art, and in particular by impregnation of the elements of groups VIII and VIB on the selected support. This impregnation may, for example, be carried out according to the method known to those skilled in the art in the dry-impregnation terminology, in which the quantity of desired elements in the form of soluble salts in the chosen solvent, for example demineralized water, so as to fill the porosity of the support as exactly as possible. The support thus filled with the solution is preferably dried.

After introduction of the elements of groups VIII and VIB, and possibly forming the catalyst, it undergoes an activation treatment. This treatment generally aims to convert the molecular precursors of the elements into an oxide phase (for example MoO ₃ ). In this case it is an oxidizing treatment but a direct reduction can also be carried out. In the case of an oxidizing treatment, also known as calcination, this is generally carried out under air or under dilute oxygen, and the treatment temperature is generally between 200 ° C. and 550 ° C., preferably between 300 ° C. C and 500 ° C. In the case of a reducing treatment, this is generally carried out under pure hydrogen or preferably diluted, and the treatment temperature is generally between 200 ° C. and 600 ° C., preferably between 300 ° C. and 500 ° C. ° C.
Group VIB and VIII metal salts which can be used in the process according to the invention are, for example, cobalt nitrate, aluminum nitrate, ammonium heptamolybdate or ammonium metatungstate. Any other known salt those skilled in the art having sufficient and decomposable solubility during the activation treatment may also be used.
The catalyst is usually used in a sulfurized form obtained after treatment in temperature in contact with a decomposable organic sulfur compound and generating H ₂ S or directly in contact with a gas stream of H ₂ S diluted in H ₂ . This step can be carried out in situ or ex situ (inside or outside the reactor) of the hydrodesulfurization reactor at temperatures between 200 and 600 ° C and more preferably between 300 and 500 ° C.

The catalysts according to the invention have a density of group VIB elements (chromium, molybdenum, tungsten) of between 4.10 ^-4 g and 36.10 ^-4 g of group VIB oxide per m ² of support, preferably between 4.10 ^-4 g and 16.10 g ^-4 oxide of the element from group VIB per m ² of support, and very preferably between 7.10 ^-4 g and 15.10 g ^-4 oxide of element from group VIB per m ² of support. The specific surface of the support should generally not exceed 200 m ² / g, and should preferably be less than 170 m ² / g and even more preferably be less than 150 m ² / g, or even less than 135 m ² /boy Wut.

It should be noted that both criteria must be generally fulfilled simultaneously as there is a synergy between these two parameters.
Without being bound by any theory, the element of group VIB and its distribution on the surface intervene in the activation and the reactivity of the molecules. It should be noted that both criteria must generally be met simultaneously because there is a synergy between these two parameters in the activation and reactivity of the molecules. Moreover, in the presence of the elements (also called metals) of the groups VIII and VIB, the surface of the support can play an important role in the mechanism of activation and surface migration of the molecules, in particular the olefins, as was recently offers [ R Prins Studies in Surface Science and Catalysis 138 p. 1-2 ]. The minimization of this activation process could possibly make it possible to limit the reactions involving olefinic compounds: hydrogenation by addition of hydrogen (penalizing for maintenance of the octane number) and recombination with H ₂ S (penalizing for desulphurisation). On the other hand, the use of significant specific surface support is problematic in the case of strongly olefinic feeds. Indeed, increasing surface acidity with the specific surface of the supports, the acid-catalysed reactions will be favored for the supports of important specific surface. Thus, the polymerization or coking reactions leading to the formation of gums or coke and finally to the premature deactivation of the catalyst will be greater on high specific surface supports. A better stability of the catalysts will be obtained for small specific surface supports.

The content of group VIII elements of the catalyst according to the invention is preferably between 1 and 20% by weight of group VIII element oxides, preferably between 2 and 10% by weight of group elements oxides. VIII and more preferably between 2 and 8% by weight of Group VIII element oxides. Preferably the group VIII element is cobalt or nickel or a mixture of these two elements, and more preferably the group VIII element consists solely of cobalt and / or nickel.

The content of Group VIB elements is preferably between 1.5 and 60% by weight of Group VIB element oxides, more preferably between 3 and 50% by weight of Group VIB group oxides. Preferably the group VIB element is molybdenum or tungsten or a mixture of these two elements, and more preferably the group VIB element consists solely of molybdenum or tungsten.

The catalyst according to the invention can be used in any process known to those skilled in the art, for desulfurizing hydrocarbon cuts of the type of catalytic cracking gasoline (FCC) for example by maintaining the octane number at high values. . It can be used in any type of reactor operated in fixed bed or mobile bed or bubbling bed, it is however preferably used in a reactor operated in fixed bed.

As an indication, the operating conditions allowing selective hydrodesulphurization of catalytic cracking gasolines are a temperature of between 200 and 400 ° C., preferably between 250 and 350 ° C., a total pressure of between 1 MPa and 3 MPa and more preferably between 1 and 3 MPa. MPa and 2.5 MPa with a ratio: volume of hydrogen per volume of charge hydrocarbon, of between 100 and 600 liters per liter and more preferably between 200 and 400 liters per liter. Finally, the Hourly Volumetric Velocity (VVH) is the inverse of the contact time expressed in hours. It is defined by the ratio of the volume flow rate of liquid hydrocarbon feedstock by the volume of catalyst charged to the reactor.

EXAMPLES Preparation of catalysts:

All molybdenum catalysts are prepared according to the same method which consists in carrying out a dry impregnation of a solution of ammonium heptamolybdate and cobalt nitrate, the volume of the solution containing the precursors of the metals being rigorously equal to the pore volume of the support mass. The supports used are transition aluminas having specific surface area and variable pore volume pairs: 130 m ² / g and 1.04 cm ³ / g; 170 m ² / g and 0.87 cm ³ / g; 220 m ² / g and 0.6 cm ³ / g; 60 m ² / g and 0.59 cm ³ / g. The precursor concentrations of the aqueous solution are adjusted so as to deposit on the support the desired weight contents. The catalyst is then dried for 12 hours at 120 ° C. and then calcined under air at 500 ° C. for 2 hours.

All tungsten catalysts are prepared by the same method which consists in carrying out a dry impregnation of a solution of ammonium metatungstate and cobalt nitrate, the volume of the solution containing the precursors of metals being strictly equal to porous volume of the support mass. The supports used are the same as before. The precursor concentrations of the aqueous solution are adjusted so as to deposit on the support the desired weight contents. The catalyst is then dried for 12 hours at 120 ° C. and then calcined under air at 500 ° C. for 2 hours.

Evaluation of catalytic performances:

A catalytic cracking gasoline (FCC) whose characteristics are summarized in Table 1 is treated by the various catalysts. The reaction is carried out by varying the temperature in the crossed-bed type reactor under the following conditions: P = 2 MPa, H ₂ / HC = 300 liters / liters of hydrocarbon feedstock, the temperature being fixed at 280 ° C. for the molybdenum catalysts and at 300 ° C for tungsten catalysts. The VVH is variable in order to compare the selectivities obtained (ratio k _HDS / k _HDO ) to iso conversion to HDS, ie for a hydrodesulphurization conversion equal to about 90% for all the catalysts. The catalysts are pretreated at 350 ° C. with a feed containing 4% by weight of sulfur in the form of DMDS (dimethyl disulphide) to ensure the sulphidation of the oxide phases. The reaction proceeds in an upward flow in an adiabatic tubular reactor. In all cases, the analysis of the residual organic sulfur compounds is carried out after removal of the H ₂ S resulting from the decomposition. The effluents are analyzed by gas chromatography for the determination of hydrocarbon concentrations and by the method described by standard NF M 07075 for the determination of total sulfur. The results are expressed as the _HDS / k _HDO speed constant ratio assuming an order 1 with respect to the sulfur compounds for the hydrodesulphurization reaction (HDS) and an order 0 with respect to the olefins for the olefin hydrogenation reaction. (HDO). For molybdenum or tungsten catalysts, the values are normalized by taking catalyst 2 or catalyst 12 as the reference, respectively. These values are given after 96 hours and 200 hours of operation in order to report respectively the initial activity and the deactivation. Table 1: Characteristics of the FCC gasoline cut. S ppm 732 Aromatic% wt 31.4 Paraffins% wt 30.4 Naphthalic% wt 6.7 Olefins% wt 31.5 PI ° C 70.5 Mp ° C 215.4

Example 1 (according to the invention):

The molybdenum catalysts according to the invention are prepared according to the procedure described above and their characteristics (density in gram of molybdenum oxide per square meter of support, contents of cobalt and molybdenum oxides of the calcined catalyst, BET surface area). support) are shown in Table 2. The K _HDS / K _HDO selectivities obtained for conversion to HDS close to 90% at the VVH mentioned are also reported in this table. Table 2: Characteristics and performances of the molybdenum catalysts according to the invention. Catalyst Density 2 g MoO ₃ / m ² % wt _CoO % MoO ₃ S BET m ² / g VVH h ^-1 k _HDS / k _HDO t = 96h K _HDS / k _HDO t = 200h 1 4.3. 10 ^-4 1.8 5.2 130 3.8 0.94 0.85 2 7.7.10 ^-4 3.1 8.8 130 4.0 1 0.94 3 14.8. 10 ^-4 5.3 15.3 130 5.3 1.32 1.21 4 35.8. 10 ^-4 5.8 16.7 60 3.4 0.85 0.81 5 7.6 .10 ^-4 3.8 11.0 170 3.1 0.78 0.71 6 16.5.10 ^{- 4} 5.8 16.6 130 3.3 0.82 0.74

Example 2 (comparative):

In this example, the density of molybdenum has been modified in order to leave the density range according to the invention. The VVH of the test is also selected in order to operate with a conversion to HDS substantially equal to 90%. Table 3 summarizes the characteristics of the catalysts and the selectivities obtained. Table 3: Characteristics and performances of comparative molybdenum catalysts tested on a catalytic cracking gasoline. Catalyst Density g MoO ₃ / m ² % wt CoO % MoO ₃ S BET m ² / g VVH h ^-1 K _HDS / K _HDO t = 48h k _HDS / k _HDO t = 200h 7 2.8.10 ^-4 1.2 3.5 130 2.4 0.59 0.56 8 37.1.10 ^-4 10.2 29.2 130 7.0 0.65 0.61

Example 3 (comparative)

In this example, the surface area of the support has been modified to be greater than 200 m ² / g. The VVH test is also selected to operate with a conversion to HDS substantially equal to 90%. Table 4 summarizes the characteristics of the catalysts and the selectivities obtained. Table 4: Characteristics and performances of the molybdenum-based comparative catalysts tested on a catalytic cracking gasoline. Catalyst Density g MoO ₃ / m ² % wt CoO % MoO ₃ S BET m ² / g VVH h ^-1 k _HDS / k _HDO t = 96h k _HDS / k _HDO t = 200h 9 7.9.10 ^-4 4.9 14.1 220 3.5 0.67 0.63 10 4.3.10 ^-4 2.9 8.4 220 1.6 0.40 0.33

Example 4 (according to the invention):

The tungsten catalysts according to the invention are prepared according to the procedure described above and their characteristics (density in grams of tungsten oxide per square meter of support, cobalt and tungsten oxide contents of the calcined catalyst, BET surface area of support) are collated in Table 5. The k _HDS / k _HDO selectivities obtained for an HDS conversion close to 90% at the mentioned VVH are also reported in this table. Table 5: Characteristics and performances of tungsten catalysts according to the invention. Catalyst Density g WO ₃ / m ² % wt CoO % wt WO ₃ S BET m ² / g VVH h ^-1 k _HDS / k _HDO t = 96h k _HDS / k _HDO t = 200h 11 4.5. 10 ^-4 1.2 5.5 130 1.5 0.93 0.88 12 8.0. 10 ^-4 2.0 9.2 130 3.0 1.00 0.95 13 14.5.10 ^-4 3.3 15.3 130 3.7 1.18 1.10 14 35.5. 10 ^-4 3.6 16.9 60 3.5 0.80 0.74 15 8.2 × 10 ^-4 2.6 11.9 170 3.2 0.88 0.82 16 16.2.10 ^-4 3.6 16.8 130 4.0 0.86 0.81

Example 5 (comparative):

In this example, the density of tungsten oxide has been modified in order to leave the density range according to the invention. The VVH of the test is also selected in order to operate with a conversion to HDS substantially equal to 90%. Table 6 summarizes the characteristics of the catalysts and the selectivities obtained. Table 6: Characteristics and performances of the comparative catalysts based on tungsten tested on a catalytic cracking gasoline. Catalyst Density gWO ₃ / m ² % wt CoO % wt WO ₃ S BET m ² / g VVH h ^-1 k _HDS / k _HDO t = 96h k _HDS / k _HDO t = 200h 17 3.1.10 ^-4 0.8 3.8 130 1.2 0.64 0.59 18 38.0 10 ^-4 6.6 30.9 130 6.5 0.60 0.55

Example 6 (comparative)

In this example, the specific surface of the support used is greater than 200 m ² / g. The VVH test is selected to operate with a conversion to HDS substantially equal to 90%. Table 7 summarizes the characteristics of the catalysts and the selectivities obtained. Table 7: Characteristics and performances of the comparative catalysts based on tungsten tested on a catalytic cracking gasoline. Catalyst Density gWO ₃ / m ² % wt CoO % wt WO ₃ S BET m ² / g VVH h ^-1 k _HDS / k _HDO t = 96h k _HDS / k _HDO t = 200h 19 8.4.10 ^-4 3.2 15.1 220 3.6 0.76 0.69 20 4.3.10 ^-4 1.8 8.5 220 2.7 0.70 0.64

Claims (10)

1. A process for the hydrodesulphurization of gasoline cuts in the presence of a catalyst comprising at least one element from group VIII, at least one element from group VIB and a support with a specific surface area of less than 200 m²/g, in which the density of the elements from group VIB per unit surface area of support is in the range 4 x 10^-4 to 36 x 10^-4 g of oxides of elements from group VIB per m² of support.
2. A hydrodesulphurization process according to claim 1, in which the density of the elements from group VIB per unit surface area of support is in the range 4 x 10^-4 g to 16 x 10^-4 g of oxides of elements from group VIB per m² of support.
3. A hydrodesulphurization process according to claim 1 or claim 2, in which the quantity of elements from group VIII of the catalyst is in the range 1% to 20% by weight of oxides of elements from group VIII and the quantity of elements from group VIB is in the range 1.5% to 60% by weight of oxides of elements from group VIB.
4. A process according to one of claims 1 to 3, in which the catalyst comprises at least one element from group VIII selected from nickel and cobalt.
5. A process according to one of claims 1 to 4, in which the catalyst comprises at least one element from group VIB selected from molybdenum and tungsten.
6. A process according to one of claims 1 to 5, in which the catalyst support is a porous solid selected from the group constituted by: aluminas, silica, silica aluminas and oxides of titanium or magnesium used alone or as a mixture with alumina or silica alumina.
7. A process according to one of claims 1 to 6, in which the catalyst support comprises at least 90% by weight of transition alumina.
8. A process according to one of claims 1 to 7, in which the feed to be hydrodesulphurized is a gasoline cut containing sulphur derived from a coking, visbreaking, steam cracking or catalytic cracking unit.
9. A process according to one of claims 1 to 8, in which the feed to be hydrodesulphurized is a gasoline cut derived from a catalytic cracking unit with a boiling point range which typically extends from the boiling points of hydrocarbons containing 5 carbon atoms to 250°C.
10. A process according to claim 9, in which the hydrodesulphurization operating conditions are a temperature in the range 200°C to 400°C, a total pressure in the range 1 MPa to 3 MPa and a volume of hydrogen per volume of hydrocarbon feed ratio in the range from 100 to 600 litres per litre.