EP1369466A1 - Hydrodesulfurization of sulphur and olefins containing fractions with a metals of groups VIII and VIB containing supported catalyst. - Google Patents

Abstract

The hydrodesulfurization of petrol cuts comprises the use of a catalyst comprising elements of groups VIII and VIB and a support of surface area less than 200 m2/g, and in which the density in group VIB element per unit of surface of the support is 4 x 10 power -4 - 36 x 10 power -4 g oxide(s) per m2 of support.

Description

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

PRIOR ART

Essence cuts and more particularly essences from FCC contain approximately 20 to 40% of olefinic compounds, 30 to 60% of aromatics and 20 to 50% of saturated compounds of paraffin or naphthene type. Among the olefinic compounds, branched olefins are predominant compared to linear and cyclic olefins. These essences also contain traces of highly unsaturated compounds of the diolefin type which are capable of deactivating the catalysts by the formation of gums. Thus, 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 elimination of sulfur. The sulfur compounds content of these gasolines is very variable depending on the type of gasoline (steam cracker, catalytic cracking, coking ...) or in the case of catalytic cracking of the severity applied to the process. It can fluctuate between 200 and 5000 ppm of S, preferably between 500 and 2000 ppm relative to the mass of filler. The families of thiophenic and benzothiophenic compounds are in the majority, the mercaptans being present only at very low levels generally between 10 and 100 ppm. FCC gasolines also contain nitrogen compounds in proportions generally not exceeding 100 ppm.
The production of reformulated gasolines meeting new environmental standards requires in particular that the concentration of olefins be reduced as little as possible in order to maintain a high octane number, but that their sulfur content is significantly reduced . Thus, current and future environmental standards oblige refiners to reduce the sulfur content in gasolines to values less than or at most equal to 50 ppm in 2003 and 10 ppm beyond 2005. These standards concern the total content of sulfur but also the nature of sulfur compounds such as mercaptans. The catalytic cracked gasolines, which can represent 30 to 50% of the gasoline pool, have high olefin and sulfur contents. Nearly 90% of the sulfur in reformulated gasolines is due to FCC gasoline. Desulfurization (hydrodesulfurization) of gasolines and mainly FCC gasolines is therefore of obvious importance for compliance with the specifications. Hydrotreating (or hydrodesulfurization) of catalytic cracking gasolines, when carried out under conventional conditions known to those skilled in the art, makes it possible to reduce the sulfur content of the cut. However, this process has the major drawback of causing a very significant drop in the octane number of the cut, due to the saturation of all the olefins during the hydrotreatment. Methods have therefore been proposed which make it possible to deeply desulfurize FCC gasolines while maintaining the octane number at a high level.

Thus, US Pat. No. 5,318,690 proposes a process consisting of fractionating the gasoline, softening the light fraction and hydrotreating the heavy fraction on a conventional catalyst and then treating it on a ZSM5 zeolite to approximately find the initial octane number. .
Patent application 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 the formation of mercaptans, involving the H ₂ S formed by the desulfurization reaction and the olefins are minimized.
Finally, US Pat. No. 5,968,346 proposes a scheme making it possible to achieve very low residual sulfur contents by a process in several stages: hydrodesulfurization 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 process but in any case the use of an intrinsically selective catalytic system is very often a key factor.

Generally, the catalysts used for this type of application are sulfide type catalysts containing an element of group VIB (Cr, Mo, W) and an element of group VIII (Fe, Ru, Os, Co, Rh , Ir, Pd, Ni, Pt). Thus in US Pat. No. 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% d '' hydrodesulfurization (HDS) against 33% hydrogenation of olefins (HDO)). Furthermore, according to US Patents 4,140,626 and US 4,774,220, it may be advantageous to add a dopant (alkali, alkaline earth) to the conventional sulfide phase (CoMoS) in order to limit the hydrogenation of olefins.

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

SUMMARY OF THE INVENTION

In the present invention, a catalyst has been found which can be used in a process. gasoline hydrodesulfurization and making it possible to reduce the total sulfur contents and in mercaptans of hydrocarbon cuts and preferably of gasoline cuts FCC, without significant loss of gasoline and minimizing the decrease in the index octane.

The invention relates more precisely to a process for hydrodesulfurization 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 of less than about 200 m ² / g, in which the density of elements of group VIB per unit area of the support is between 4.10 ^-4 and 36.10 ^-4 g of oxides of elements of group VIB per m ² of support.

DETAILED DESCRIPTION OF THE INVENTION

The feed to be hydrotreated (or hydrodesulfurized) by means of the process according to the invention is generally a gasoline cut containing sulfur; such as for example a section from a coking unit (coking according to Anglo-Saxon terminology), visbreaking (visbreaking according to Anglo-Saxon terminology), steam cracking (steam cracking according to Anglo-Saxon terminology) or catalytic cracking (FCC, Fluid Catalytic Cracking according to Anglo-Saxon terminology). The said charge is preferably made of a petrol cut from a cracking unit catalytic whose range of boiling points typically extends from points boiling of hydrocarbons with 5 carbon atoms up to about 250 ° C. This gasoline can possibly be composed of a significant fraction of gasoline from other production processes such as atmospheric distillation (gasoline from direct distillation (or straight run gasoline according to terminology Anglo-Saxon) or conversion processes (essence of coking or steam cracking).

The hydrodesulfurization catalysts according to the invention are catalysts comprising at least one element from group VIB and at least one element from group VIII on a suitable support. The element or elements of group VIB are preferably chosen from molybdenum and / or tungsten and the element or elements of group VIII are of preferably chosen from nickel and / or cobalt. The catalyst support is usually a porous solid chosen from the group consisting of: aluminas, silica, alumina silicas or titanium or magnesium oxides used alone or mixed with alumina or silica alumina. It is preferably chosen from the group consisting of: silica, the family of transition aluminas and silicas alumina, very preferably, the support is essentially constituted by at minus a transition alumina, that is to say it comprises at least 51% by weight, of preferably at least 60% by weight very preferably at least 80% by weight, or even at least 90% by weight of transition alumina. It can possibly be constituted only a transition alumina.

The specific surface of the support according to the invention is generally less than approximately 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. The support can be prepared using any precursor, any preparation method and any shaping tool known to those skilled in the art.

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

After introduction of the elements of groups VIII and VIB, and possibly shaping of the catalyst, the latter undergoes an activation treatment. This treatment generally aims to transform the molecular precursors of the elements in the 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 called calcination, this is generally carried out in air or under dilute oxygen, and the treatment temperature is generally between 200 ° C and 550 ° C, preferably between 300 ° C and 500 ° C. In the case of a reducing treatment, this is generally carried out under pure or preferably diluted hydrogen, and the treatment temperature is generally between 200 ° C and 600 ° C, preferably between 300 ° C and 500 ° C.
Metal salts of groups VIB and VIII 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 salt known to a person skilled in the art having sufficient solubility and which can be broken down during the activation treatment can also be used.
The catalyst is usually used in a sulfurized form obtained after temperature treatment in contact with a decomposable sulfur-containing organic compound and generator of H ₂ S or directly in contact with a gaseous flow 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 elements of group VIB (chromium, molybdenum, tungsten) of between 4.10 ^-4 g and 36.10 ^-4 g of oxide of the element of group VIB per m ² of support, preferably between 4.10 ^-4 g and 16.10 ^-4 g of oxide of the element of group VIB per m ² of support, and very preferably between 7.10 ^-4 g and 15.10 ^-4 g of oxide of the element of group VIB per m ² of support. The specific surface of the support must generally not exceed approximately 200 m ² / g, and must 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 / g.

It should be noted that the two criteria must generally be fulfilled simultaneously since 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 reactivity of molecules. It should be noted that the two criteria must generally be fulfilled simultaneously since there is a synergy between these two parameters in the activation and reactivity of the 5 molecules. Furthermore, in the presence of elements (also called metals) of groups VIII and VIB, the surface of the support can play an important role in the mechanism of activation and surface migration of molecules, in particular olefins, as has been recently proposed [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 maintaining the octane number) and recombination with H ₂ S (penalizing for desulfurization). On the other hand, the use of a support of large specific surface is problematic in the case of highly olefinic fillers. Indeed, the surface acidity increasing with the specific surface of the supports, the catalyzed acido reactions will be favored for the supports of large specific surface. Thus, the polymerization or coking reactions leading to the formation of gums or coke and ultimately to the premature deactivation of the catalyst will be greater on supports with a high specific surface. Better stability of the catalysts will be obtained for supports with a small specific surface.

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

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

The catalyst according to the invention can be used in any process known to man of the trade, making it possible to desulfurize hydrocarbon cuts of the gasoline type catalytic cracking (FCC) for example by keeping the octane number at values high. It can be used in any type of reactor operated in a fixed bed or in a bed mobile or in a bubbling bed, it is however preferably used in a reactor operated on a fixed bed.

As an indication, the operating conditions allowing selective hydrodesulfurization catalytic cracked gasolines are a temperature between about 200 and about 400 ° C, preferably between about 250 and about 350 ° C, a total pressure between 1 MPa and 3 MPa and more preferably between approximately 1 MPa and approximately 2.5 MPa with a ratio: volume of hydrogen per volume of charge hydrocarbon, between approximately 100 and approximately 600 liters per liter or more preferably between about 200 and about 400 liters per liter. Finally, the Speed Hourly Volume (VVH) is the inverse of the contact time expressed in hours. She is defined by the ratio of the volume flow rate of liquid hydrocarbon feedstock by the volume of catalyst loaded into the reactor.

EXAMPLES Catalyst preparation:

All molybdenum-based catalysts are prepared according to the same method which consists in carrying out a dry impregnation of a solution of ammonium heptamolybdate and of cobalt nitrate, the volume of the solution containing the metal precursors being strictly equal the pore volume of the support mass. The supports used are transition aluminas having variable surface area and pore volume couples: 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 concentrations of precursors of the aqueous solution are adjusted so as to deposit the desired weight contents on the support. The catalyst is then dried for 12 hours at 120 ° C and then calcined in air at 500 ° C for 2 hours.

All tungsten catalysts are prepared using the same method which consists in carrying out a dry impregnation of a metatungstate solution ammonium and cobalt nitrate, the volume of the solution containing the precursors metals being strictly equal to the pore volume of the support mass. The supports used are the same as before. The concentrations in precursors 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 then calcined in air at 500 ° C for 2 hours.

Evaluation of catalytic performances:

A catalytic cracking gasoline (FCC), the characteristics of which are collated in Table 1, is treated by the various catalysts. The reaction is carried out by varying the temperature in a bed-type reactor crossed 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-based catalysts, and 300 ° C for the tungsten-based catalysts. The VVH is variable in order to compare the selectivities obtained (k _HDS / k _HDO ratio) with iso conversion to HDS, ie for a conversion into hydrodesulfurization equal to approximately 90% for all the catalysts. The catalysts are previously treated at 350 ° C. with a feed containing 4% by weight of sulfur in the form of DMDS (dimethyldisulfide) to ensure the sulfurization of the oxide phases. The reaction takes place in an updraft in an adiabatic tubular reactor. In all cases, the analysis of the residual organic sulfur compounds is carried out after elimination 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 a rate constant k _HDS / k _HDO assuming an order 1 with respect to the sulfur compounds for the hydrodesulfurization reaction (HDS) and an order 0 with respect to the olefins for the hydrogenation reaction for the olefins (HDO). For molybdenum or tungsten based catalysts, the values are normalized using catalyst 2 or catalyst 12 respectively as a reference. These values are given after 96 hours and 200 hours of operation in order to report respectively the initial activity and the deactivation. characteristics of the FCC petrol cutter. S ppm 732 Aromatic% wt 31.4 Paraffins% wt 30.4 Naphthenic% wt 6.7 Olefins% wt 31.5 PI ° C 70.5 Mp ° C 215.4

Example 1 (according to the invention):

The molybdenum-based catalysts according to the invention are prepared according to the procedure described above and their characteristics (density in grams of molybdenum oxide per square meter of support, contents of cobalt and molybdenum oxides of the calcined catalyst, BET surface of the support) are collated in Table 2. The selectivities K _HDS / K _HDO obtained for a conversion into HDS close to 90% at the mentioned VVH are also reported in this table. Characteristics and performances of the molybdenum catalysts according to the invention. Catalyst Catalyst Density 2 g MoO ₃ / m ² % wt _CoO % w MoO ₃ S BET m ² / g VVH h ^-1 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 range of densities 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. Characteristics and performance of comparative molybdenum catalysts tested on catalytic cracking gasoline. Catalyst Catalyst Density g MoO ₃ / m ² % wt CoO % wt MoO ₃ m ² / g S BET VVH h ^-1 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 specific surface of the support has been modified to be greater than 200 m ² / g. The test VVH is also selected in order to operate with a conversion to HDS substantially equal to 90%. Table 4 summarizes the characteristics of the catalysts and the selectivities obtained. Characteristics and performance of comparative molybdenum catalysts tested on catalytic cracking gasoline. Catalyst Density ₂ g MoO ₃ / m ² % wt CoO % wt MoO ₃ m2 / g S BET VVH h ^-1 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, contents of cobalt and tungsten oxides of the calcined catalyst, BET surface of the support) are collated in table 5. The selectivities k _HDS / k _HDO obtained for a conversion into HDS close to 90% at the mentioned VVH are also reported in this table. Characteristics and performances of the tungsten catalysts according to the invention. Catalyst Catalyst Density g WO ₃ / m ² % wt CoO % wt WO ₃ S BET m ² / g _VVH h ^-1 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 range of densities 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. Characteristics and performance of comparative tungsten catalysts tested on catalytic cracked gasoline. Catalyst Catalyst Density gWO ₃ / m ² % wt CoO % wt WO ₃ S BET m ² / g VVH h ^{-1 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 test VVH is selected in order to operate with a conversion to HDS substantially equal to 90%. Table 7 summarizes the characteristics of the catalysts and the selectivities obtained. Characteristics and performance of comparative tungsten catalysts tested on catalytic cracked gasoline. Catalyst Catalyst Density gWO ₃ / m ² % wt CoO % wt WO ₃ S BET m ² / g ^VVH h ^-1 kHDS / 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)

Process for hydrodesulfurization 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 of less than about 200 m ² / g, in which the density in elements of group VIB per unit area of the support is between 4.10 ^-4 and 36.10 ^-4 g of oxides of elements of group VIB per m ² of support. Hydrodesulfurization process according to claim 1, in which the density of elements of group VIB per unit area of the support is between 4.10 ^-4 g and 16.10 ^-4 g of oxides of elements of group VIB per m ² of support. Hydrodesulfurization process according to either of Claims 1 and 2, in which the content of elements of group VIII of the catalyst is between 1 and 20% by weight of group VIII element oxides and the group VIB content is between 1.5 and 60% by weight of oxides of elements from group VIB. Method according to one of claims 1 to 3 wherein the catalyst comprises at least one element of group VIII chosen from nickel and cobalt. Process according to one of Claims 1 to 4, in which the catalyst comprises at least one element from group VIB chosen from molybdenum and tungsten. Process according to one of Claims 1 to 5, in which the support for the catalyst is a porous solid chosen from the group consisting of: aluminas, silica, alumina silicas or titanium or magnesium oxides used alone or in mixture with alumina or silica alumina. Process according to one of Claims 1 to 6, in which the support for the catalyst comprises at least 90% by weight of transition alumina. Method according to one of claims 1 to 7 wherein the charge to hydrodesulfurizer is a gasoline cut containing sulfur resulting from a unit of coking, visbreaking, steam cracking, or catalytic cracking. Method according to one of claims 1 to 8 wherein the charge to hydrodesulfurizer is a petrol cut from a catalytic cracking unit whose range of boiling points typically extends from the boiling points of hydrocarbons with 5 carbon atoms up to around 250 ° C. The method of claim 9 wherein the operating conditions hydrodesulfurization are a temperature between about 200 and about 400 ° C, a total pressure between 1 MPa and 3 MPa, and a ratio: volume of hydrogen per volume of hydrocarbon feedstock, between approximately 100 and about 600 liters per liter.