EP1369468A1 - Process of production of hydrocarbons with low content of sulfur and of nitrogen - Google Patents

Abstract

In the desulfurization of petrol charges comprising at least 150 ppm of sulfur compounds by a hydrodesulfurization catalyst, the charge is submitted to a pre-treatment of deazotization in conditions such that the content of nitrogen compounds at the time of contact with the catalyst does not exceed 150 ppm. An Independent claim is also included for the application of the process to petrol derived form heavy hydrocarbons.

Description

The present invention relates to a process for producing hydrocarbons with a low content of sulfur. This fraction of hydrocarbons contains a generally higher fraction of olefins at 5% by weight and more often than 10% by weight, a sulfur content greater than 100 ppm by weight and a nitrogen content greater than 20 ppm by weight. The process allows in particular to recover the entire petrol cut containing sulfur by reducing sulfur contents of said petrol cut at very low levels, without reducing the gasoline yield, and minimizing the decrease in octane number during said process. The invention finds its application particularly when the essence to be treated is a cracked gasoline containing a sulfur content greater than 300 ppm by weight or even greater than 500 ppm, and a nitrogen content generally greater than 50 ppm by weight, or even greater than 100 ppm by weight and preferably greater than 150 ppm by weight, or even 200 ppm by weight or even more.

Future specifications for automotive fuels forecast a sharp decrease in sulfur content in these fuels, and in particular on gasoline. This decrease is intended to limit, in particular the content of sulfur and nitrogen oxide in the gases automobile exhaust. The current sulfur content specifications are around 150 ppm weight and will decrease in the coming years to reach contents below 10 ppm after a transition to 30 ppm by weight. The evolution of specifications of sulfur content in fuels thus requires the development of new processes for deep desulphurization of gasolines.

The main sources of sulfur in gasoline bases are the so-called cracking, and mainly, the gasoline fraction from a catalytic cracking process a residue from the atmospheric or vacuum distillation of crude oil. The petrol fraction from catalytic cracking, which represents on average 40% of petrol bases, contributes in fact for more than 90% the contribution of sulfur in gasolines. Therefore, the production of low sulfur gasoline requires a step of desulfurization of gasoline catalytic cracking. This desulfurization is conventionally carried out by one or more stages of bringing the sulfur compounds contained in said gasolines into contact with a rich gas into hydrogen in a process known as hydrodesulfurization.

Furthermore, the octane number of such gasolines is very strongly linked to their olefin content. Preserving the octane number of these species therefore requires limiting the reactions of transformation of olefins into paraffins which are inherent in the processes hydrodesulfurization.

When the gasoline is desulfurized in a conventional manner, the reactions of saturation of the olefins which occur in parallel with the reactions of transformation of the sulfur-containing compounds into H ₂ S lead to a high loss in octane. In a context of restriction of sulfur standards in gasolines, such processes lead to unacceptable octane losses. Many solutions have been proposed for selectively eliminating the sulfur-containing compounds in gasolines by limiting the undesirable reactions of hydrogenation of olefins, generally evaluated by a person skilled in the art in the form of a saturation rate of olefins at the outlet of the reactor. However, the impact of nitrogen compounds on the activity and / or selectivity of gasoline hydrodesulfurization catalysts is very little known.

We do know, however, in the case of hydrotreating middle distillates (diesel and kerosene), that the presence of nitrogen compounds inhibits hydrodesulfurization reactions. For example, a process for the production of middle distillates with a low sulfur content has been proposed, comprising a step of removing basic nitrogen before the hydrotreatment step (Proc. Int. Conf. Stab. Handl. Liq. Fuels, 7th, meeting date 2000, Vol. 1, 153-163). This step elimination of basic nitrogen is said to be necessary for obtaining high desulfurization rates. However, the technical problems posed by the hydrodesulfurization of gasolines appear different from those posed by the hydrodesulfurization of middle distillates in particular because difficulties inherent in the presence of unsaturated compounds in gasolines and specific problem of loss of octane previously described.

Thus in the particular case of essences, US patent 6,120,679 teaches a contrario method for preparing hydrodesulfurization catalysts based on a pre-treatment step catalysts with a nitrogen compound (pyridine).

The work carried out by the applicant and subject of this request resulted in demonstrate that the presence of nitrogen in significant quantities, i.e. at rates greater than those previously described, had a significant effect on the activity of the catalyst of hydrodesulfurization of gasolines and that in particular the presence beyond a certain threshold of basic nitrogen compounds such as for example pyridine resulted in the degradation not only of the activity but also of the selectivity of the catalysts hydrodesulfurization. In particular, it has been found by the applicant that disposal in certain proportions of these nitrogen compounds had a very noticeable effect on decomposition compounds sulfur-containing by the catalyst, but a relatively limited effect on hydrogenation unsaturated compounds. According to a possible mode of application of the present invention, for the same saturation rate of olefins leaving the reactor and for the same temperature of the hydrodesulfurization reactor, it will be possible to increase the activity of the catalyst thanks to a prior reduction in the nitrogen compounds present in the species. According to another mode of application of the present invention, the elimination of basic nitrogen compounds before hydrodesulfurization will limit the saturation rate olefins for a fixed sulfur content at the outlet of the reactor. The present invention finds thus particularly its application in the treatment of gasoline cuts having a strong nitrogen compound rate.

• d'atteindre les spécifications futures sur les essences pour automobile, c'est à dire des teneurs en soufre de l'ordre de 50 ppm voire moins de 10 ppm selon les pays,
• de limiter la teneur en azote dans les essences,
• de contrôler les processus d'hydrogénation des oléfines au cours dudit procédé,
• de limiter par suite la perte d'indice octane liée aux procédés d'hydrodésulfuration,
• de maximiser la durée de vie des catalyseurs d'hydrodésulfuration en mettant en oeuvre les réacteurs d'hydrodésulfuration à plus basse température.

In general, the present invention relates to a method allowing both:

• to meet future specifications for gasolines for cars, that is to say sulfur contents of the order of 50 ppm or even less than 10 ppm depending on the country,
• limit the nitrogen content in gasolines,
• to control the hydrogenation processes of olefins during said process,
• consequently limit the loss of octane index linked to hydrodesulfurization processes,
• to maximize the lifetime of the hydrodesulfurization catalysts by using hydrodesulfurization reactors at a lower temperature.

In summary, the present desulfurization process offers a solution to achieve strong desulfurization rate, while limiting the loss of octane by hydrogenation of olefins. It results in the production of a gasoline low in sulfur and with a high octane number.

The present invention is a process for desulfurization of a gasoline charge comprising at least minus 150 ppm by weight of sulfur-containing compounds by a hydrodesulfurization catalyst, said process being characterized in that said load is subjected to a prior treatment of denitrogenation under conditions such as the level of nitrogen compounds present within said charge at the time of contacting with said hydrodesulfurization catalyst does not exceed 150 ppm weight.

According to a possible embodiment of the invention, the denitrogenation treatment is carried out immediately before said contacting (hydrodesulfurization).

a) l'hydrogénation sélective des diènes contenus dans la charge,

b) la transformation des composés soufrés légers contenus dans la charge,

c) la séparation de ladite charge en au moins deux fractions dont:

• une fraction légère contenant une mineure partie des composés soufrés,
• une fraction lourde contenant la majeure partie des composés soufrés,

est effectuée avant ledit traitement de déazotation (étape d).

Thus according to a first embodiment, for example when said treatment is carried out immediately before said contacting (step e and possibly f), at least one step chosen from the group consisting of:

a) the selective hydrogenation of the dienes contained in the feed,

b) the transformation of the light sulfur compounds contained in the feed,

c) the separation of said charge into at least two fractions, of which:

• a light fraction containing a minor part of the sulfur compounds,
• a heavy fraction containing the major part of the sulfur compounds,

is carried out before said denitrogenation treatment (step d).

a) l'hydrogénation sélective des diènes contenus dans la charge,

b) la transformation des composés soufrés légers contenus dans la charge,

c) la séparation de ladite charge en au moins deux fractions dont:

• une fraction légère contenant une mineure partie des composés soufrés,
• une fraction lourde contenant la majeure partie des composés soufrés,

est effectuée entre ledit traitement de déazotation (étape d) et ladite mise en contact (étape e et éventuellement f).

Advantageously, said contacting (step e is optionally f) is then carried out at least and / or preferably with the heavy fraction resulting from step c).
According to an alternative embodiment, at least one step chosen from the group consisting of:

a) the selective hydrogenation of the dienes contained in the feed,

b) the transformation of the light sulfur compounds contained in the feed,

c) the separation of said charge into at least two fractions, of which:

• a light fraction containing a minor part of the sulfur compounds,
• a heavy fraction containing the major part of the sulfur compounds,

is carried out between said denitrogenation treatment (step d) and said contacting (step e and possibly f).

Advantageously, said contacting (hydrodesulfurization) is then carried out at least and / or preferably with the heavy fraction from step c).

Preferably, said contacting is for example carried out in at least two steps e) and f), whatever the embodiment envisaged.

In general, said hydrodesulfurization catalyst comprises at least one element from group VIII of the periodic table and advantageously, said hydrodesulfurization catalyst includes at least one element from group VIB of the periodic table.

Preferably, said element of group VIII of the classification is chosen from the group. consisting of Nickel and Cobalt and at least at least one element of group VIB of the classification chosen from the group consisting of Molybdenum and Tungsten.

The conditions for said contacting are generally as follows: a temperature between 200 ° C and 450 ° C, a pressure between 1 and 3 MPa, a liquid hourly space velocity between 1h ^-1 and 10h ^-1 and a ratio H2 / HC (hydrogen to hydrocarbons ratio expressed in liters per liter) between 50 l / l and 500 l / l.

The present process can advantageously be applied to gasolines from cracking catalytic or coking of a heavy hydrocarbon feed or steam cracking.

The invention will be better understood on reading the following embodiment, given as purely illustrative and not limiting of the invention:

According to a preferred but not compulsory embodiment of the invention, the charge to be desulfurized is optionally pretreated in a sequence of hydrogenation reactors selective diolefins (step a) and weighting of light sulfur compounds (step b). The charge thus possibly pretreated is then distilled and fractionated into at least two cuts (step c): a light essence low in sulfur and rich in olefins and an essence heavy rich in sulfur and depleted in olefins. The light fraction from the three stages generally contain less than 100 ppm sulfur, preferably less than 50 ppm of sulfur, and very preferably, less than 20 ppm of sulfur, and does not require generally no further treatment before its incorporation as a petrol base. Fraction heavy from the previous three stages which concentrates most of the sulfur is treated according to the process which is the subject of the present invention. This preferred embodiment presents the advantage of further minimizing the loss of octane because light olefins with 5 atoms of carbon, easily hydrogenated, is not sent to the hydrodesulfurization section.

Step a) is optional and is mainly intended to eliminate the diolefins present in essence. This step notably makes it possible to maximize the lifetime of the catalysts used in the steps downstream. Steps b) and c) are also optional, but they allow, if they are carried out before step e), to minimize the octane loss on the whole process.

Step d) of denitrogenation is carried out before contacting with the catalyst hydrodesulfurization (steps e and / or f) or before at least one of steps a), b), and / or c), in order that the level of nitrogen compounds does not exceed 150 ppm (expressed by weight), preferably 125 ppm, more preferably 100 ppm.

The method according to the invention comprises at least the two stages d) and e). Step d) corresponds to a step of at least partial elimination of the nitrogen contained in the gasolines, stage e) corresponds to a hydrotreatment stage of the gasoline thus pretreated.

In general the experimental conditions of these stages a) to f) of pretreatment, denitrogenation or hydrodesulfurization are as follows:

1 °) Selective hydrogenation (step a):

This optional step of pre-treatment of the gasoline to be desulfurized is intended to eliminate the less partially the diolefins present in gasoline. The hydrogenation of the dienes is an optional but advantageous step, which eliminates the vast majority of dienes present in the cut to be treated before hydrotreating. Diolefins are precursors of gums which polymerize in hydrotreatment reactors and limit their lifespan.

This step generally takes place in the presence of a catalyst comprising at least one metal from group VIII, preferably chosen from the group formed by platinum, palladium and nickel, and a support. Use will be made, for example, of a catalyst containing 1 to 20% by weight of nickel deposited on an inert support, such as, for example, alumina, silica, silica-alumina, a nickel aluminate or a support containing at least 50% alumina. This catalyst operates under a pressure of 0.4 to 5 MPa, at a temperature of 50 to 250 ° C, with an hourly space velocity of the liquid from 1 h ^-1 to 10 h ^-1 . Another group VIB metal can be combined to form a bimetallic catalyst, such as, for example, molybdenum or tungsten. This group VIB metal, if it is associated with group VIII metal, will be deposited at a level of 1% by weight to 20% by weight on the support.

The choice of operating conditions is particularly important. We will operate the most generally under pressure in the presence of a small amount of hydrogen by compared to the stoichiometric value necessary to hydrogenate the diolefins. Hydrogen and the charge to be treated is injected in updrafts or downdrafts in a reactor preferably with a fixed catalyst bed. The temperature is most generally between 50 and 300 ° C, and preferably between 80 and 250 ° C, and preferably between 120 and 210 ° C.

The pressure is most generally from 0.4 to 5 MPa and preferably greater than 1 MPa. A advantageous pressure is between 1 to 4 MPa, terminals included.

The space speed is, in these conditions of the order of 1 to 12 h ^-1 , preferably of the order of 4 to 10 h ^-1 .

The light fraction of the gasoline catalytic cracking cut can contain up to a few% by weight of diolefins. After hydrogenation, the diolefin content is reduced to less than 3000 ppm, or even less than 2500 ppm and better still less than 1500 ppm. In some case, it can be obtained less than 500 ppm. The content of dienes after selective hydrogenation can even be reduced to less than 250 ppm.

Concomitantly with the selective hydrogenation reaction of the diolefins, a isomerization of the double bond of external olefins leading to the formation of olefins internal. This isomerization results in the formation of olefins more refractory to saturation with hydrogen and a slight gain in octane number (or compensation for octane number due to low olefin loss). This is due to the fact that internal olefins have an octane number generally higher than that of terminal olefins.

According to one embodiment of the invention, the hydrogenation step of the dienes takes place in a catalytic hydrogenation reactor which comprises a crossed catalytic reaction zone preferably by the totality of the charge and by the quantity of hydrogen necessary for carry out the desired reactions.

Certain nitrogen compounds are also transformed during this stage. It's the case, for example weakly basic nitriles which, by hydrogenation, are transformed into amines which have a higher basicity.

2 °) Transformation of light sulfur compounds (step b):

This optional step consists in transforming the light saturated sulfur compounds, that is to say the compounds whose boiling point is lower than that of thiophene, into saturated sulfur compounds whose boiling point is higher than that of thiophene . These light sulfur compounds are typically mercaptans of 1 to 5 carbon atoms, CS ₂ and sulfides comprising of 2 to 4 carbon atoms. This transformation is preferably carried out on a catalyst comprising at least one element from group VIII (groups 8, 9 and 10 of the new periodic classification) on a support of alumina, silica or silica alumina or nickel aluminate type. The choice of catalyst is made in particular so as to promote the reaction between light mercaptans and olefins, which leads to mercaptans or sulphides with boiling temperatures higher than thiophene.

This optional step can optionally be carried out at the same time as step a), in the same reaction bed and by the same catalyst. For example, it can be particularly advantageous to operate, during the hydrogenation of diolefins, under conditions such as at least part of the compounds in the form of mercaptans are transformed.

In this case the temperatures are generally between 100 and 300 ° C and preferably between 150 and 250 ° C. The H ₂ / charge ratio is adjusted between 1 and 20 liters per liter, preferably between 3 and 15 liters per liter. The space velocity is generally between 1 and 10 h ^-1 , preferably between 2 and 6 h ^-1 and the pressure between 0.5 and 5 MPa, preferably between 1 and 3 MPa.

The nitrogen compounds present in petrol are also partly weighed down during this step. Indeed, it has been found by the inventors that the nitrogen compounds present in the PI fraction (initial point) -60 ° C were transformed into heavier nitrogen compounds boiling point above 60 ° C. Step b) therefore makes it possible to separate a part of the nitrogen compounds of the PI-60 ° C fraction.

3) separation of the essence into at least two fractions (step c):

• une fraction légère contenant une teneur en soufre résiduelle limitée, de préférence inférieure à environ 50 ppm, de manière préférée inférieure à environ 20 ppm, de manière très préférée inférieure à environ 10 ppm, et permettant d'utiliser cette coupe sans effectuer d'autre(s) traitement(s) visant à diminuer sa teneur en soufre; cette fraction légère étant également appauvrie en composés azotés légers,
• une fraction lourde dans laquelle la majeure partie du soufre, c'est à dire la totalité du soufre qui ne se trouve pas dans l'essence légère, initialement présent dans la charge est concentrée.

This optional step, carried out after steps a) and b), makes it possible to produce a light desulfurized gasoline, generally containing less than 5 ppm of mercaptans. During this step, the essence is split into at least two fractions:

• a light fraction containing a limited residual sulfur content, preferably less than approximately 50 ppm, preferably less than approximately 20 ppm, very preferably less than approximately 10 ppm, and allowing this cut to be used without making any other (s) treatment (s) aimed at reducing its sulfur content; this light fraction also being depleted in light nitrogen compounds,
• a heavy fraction in which most of the sulfur, ie all of the sulfur which is not found in light petrol, initially present in the charge is concentrated.

This separation is preferably carried out by means of a conventional distillation column. This fractionation column must make it possible to separate a light fraction of the gasoline containing a small fraction of sulfur and a heavy fraction preferably containing the most of the sulfur initially present in the original gasoline.

The light gasoline obtained after separation generally contains at least the whole olefins with five carbon atoms, preferably compounds with five carbon atoms and at least 20% of the olefins with six carbon atoms. Generally this light fraction obtained after steps a) and b) has a low sulfur content, that is to say that it is not generally not necessary to treat the light cut before using it as fuel.

4 °) Elimination of nitrogen in gasolines: step d)

The nitrogen compounds present in gasolines mainly belong to the families following: nitriles, amines, pyroles, pyridines and anilines. These compounds are generally present at 20 to 400 ppm in gasolines. These compounds are for the most part basic, they can therefore be eliminated by separation in an acid medium. The elimination step of nitrogen in gasoline can therefore consist of washing the gasoline with a solution aqueous containing an acidic compound. Among the acids used, let us quote phosphoric acid, sulfuric acid, hydrochloric acid or formic acid. Any type of water-soluble acid and whose acidity is sufficient to protonate nitrogen can be used for this operation. This operation is carried out by bringing the essence to be treated into contact with the acid, for example, in a washing column. The washing conditions are optimized so that the recovered petrol contains less than 150 ppm nitrogen, preferably less than 100 ppm nitrogen, and more preferably, less than 50 ppm of nitrogen, or even less than 20 ppm.

Step d) can also be carried out by treating the gasoline on a solid having a Lewis or Bronsted acidity sufficient to fix the nitrogen compounds. The solids that can be used are, for example, ion exchange resins, strong acids on mineral support such as phosphoric acid on silica, silica aluminas in the form zeolitic or amorphous. This list is given for illustration only, and we would not get out of the framework of the present invention using any other known technique aimed at eliminating all or part of the nitrogen compounds present in a hydrocarbon fraction. The gasoline crosses a guard mass generally used in a fixed bed, the basic nitrogen compounds protonate and are fixed to the mass. Once saturated, the mass can be regenerated or more simply replaced by a new mass.

The choice of mass, its duration of use and the operating conditions are optimized for the gasoline produced during step d) contains less than 150 ppm of nitrogen, or even 100 ppm nitrogen, and more preferably less than 50 ppm nitrogen, and more preferably less 20 ppm nitrogen. According to another way of implementing the invention, the choice of the mass, its duration of use and the operating conditions are optimized so that at least 50%, preferably 70% and very preferably at least 90% of the nitrogen compounds are eliminated during this step.

An advantageous embodiment of the invention consists in carrying out step a) before step d). Indeed, certain nitrogen compounds such as nitriles are transformed during step a) to form the corresponding amines. The reaction observed is as follows: CH3-CH2-CN + 2 H ₂ → CH3-CH2-CH ₂ -NH ₂

Amines being more basic than nitriles, their extraction during step d) will be facilitated.

• la fraction légère qui concentre les oléfines et qui est appauvrie en azote,
• la fraction lourde qui concentre l'azote basique et les aromatiques et qui est appauvrie en oléfines.

Step d) can also comprise a separation, generally by distillation, of the gasoline to be treated. Indeed, the basic compounds present in cracked gasolines are concentrated in the heavy fraction of the gasoline. The elimination of this heavy fraction by distillation therefore makes it possible to at least partially eliminate the basic nitrogen compounds. In this case, step d) which consists of a distillation produces at least two fractions:

• the light fraction which concentrates the olefins and which is depleted in nitrogen,
• the heavy fraction which concentrates basic nitrogen and aromatics and which is depleted in olefins.

5 °) Hydrodesulfurization of gasolines: step e)

The hydrodesulfurization step (step e) consists in passing the gasoline to be treated in the presence of hydrogen, over a hydrodesulfurization catalyst, at a temperature between 200 ° C and 350 ° C, preferably between 250 ° C and 320 ° C and at a pressure between 1 and 3 MPa, preferably between 1.5 and 2.5 MPa. The liquid space velocity is generally between 1 h ^-1 and 10 h ^-1 , preferably between 2 h ^-1 and 5 h ^-1 , the H ₂ / HC ratio is between 50 liters / liter (l / l) and 500 l / l, preferably between 100 l / l and 450 l / l, and more preferably between 150 l / l and 400 l / l. The H ₂ / HC ratio is the ratio between the flow of hydrogen under 1 atmosphere and 0 ° C. and the flow of hydrocarbon. Under these conditions, the reaction takes place in the gas phase. The operating conditions during this stage are therefore adjusted as a function of the characteristics of the feed to be treated in order to achieve a desired desulfurization rate. The effluents from this hydrodesulfurization step are partially desulfurized gasoline, residual hydrogen and H ₂ S produced by decomposition of the sulfur compounds.

The catalysts used during step e) comprises at least one element from group VIII and / or at least one element from group VIB on an appropriate support.

The content of group VIII metal expressed as oxide is generally between 0.5 and 15% by weight, preferably between 1 and 10% by weight. The metal content of group VIB is generally between 1.5 and 60% by weight, preferably between 3 and 50% by weight.

The element of group VIII, when it is present, is preferably cobalt, and the element of group VIB, when it is present, is generally molybdenum or tungsten. The catalyst support is usually a porous solid, such as for example an alumina, a silica-alumina or other porous solids, such as for example magnesia, silica or titanium oxide, alone or in combination. mixture with alumina or silica-alumina. To minimize the hydrogenation of olefins present in heavy gasoline, it is advantageous to preferably use a catalyst in which the density of molybdenum, expressed as% by weight of MoO ₃ per unit area is greater than 0.07 and preferably greater at 0.10. The catalyst according to the invention preferably has a specific surface of less than 200 m ² / g, more preferably less than 180 m ² / g, and very preferably less than 150 m ² / g.

The catalyst is preferably used at least in part in its sulfurized form. The sulfur or a sulfur-containing compound can be introduced ex situ, that is to say outside the reactor where the process according to the invention is carried out, or in situ, that is to say in the reactor used for the process according to the invention. Sulfurization consists in passing a charge containing at least one sulfur compound, which once decomposed leads to the fixing of sulfur on the catalyst. This charge can be gaseous or liquid, for example hydrogen containing H ₂ S, or a liquid containing at least one sulfur-containing compound.

6 °) Hydrodesulfurization of gasolines: step f)

The hydrodesulfurization step e) can be followed by an additional step aimed at improving the final desulfurization rate. This step is necessarily carried out after step e) and can be carried out with or without intermediate elimination of H ₂ S. Step f) comprises at least one step of decomposition of the saturated sulfur compounds originating from step e). These sulfur compounds are transformed into H ₂ S over a catalyst and under conditions such that the olefins are very little hydrogenated. The rate of hydrogenation (saturation) of the olefins in this step is generally less than 20%, and preferably, less than 10%.

This hydrodesulfurization step (step f) generally consists in passing the gasoline to be treated in the presence of hydrogen, over a hydrodesulfurization catalyst, at a temperature between 250 ° C and 450 ° C, preferably between 300 ° C and 360 ° C and at a pressure between 1 and 3 MPa, preferably between 1.5 and 2.5 MPa. The liquid space velocity is generally between 1 h ^-1 and 10 h ^-1 , preferably between 1 h ^-1 and 5 h ^-1 , the H ₂ / HC ratio is between 50 liters / liter (l / l) and 500 l / l, preferably between 100 l / l and 450 l / l, and more preferably between 150 l / l and 400 l / l. Under these conditions, the reaction takes place in the gas phase. The operating conditions during this stage are therefore adjusted as a function of the characteristics of the feed to be treated in order to achieve a desired desulfurization rate.

The catalyst used during step e) comprises at least one element from group VIII chosen in the group formed by nickel, cobalt, iron, molybdenum and tungsten.

The content of group VIII metal expressed as oxide is generally between 1 and 60% by weight, preferably between 1 and 40% by weight.

The catalyst support is usually a porous solid, such as for example an alumina, a silica-alumina or other porous solids, such as for example magnesia, silica or titanium oxide, alone or in combination. mixture with alumina or silica-alumina. The catalyst according to the invention preferably has a specific surface of between 25 and 350 m ² / g.

The catalyst is preferably used at least in part in its sulfurized form. The sulfur or a sulfur-containing compound can be introduced ex situ, that is to say outside the reactor where the process according to the invention is carried out, or in situ, that is to say in the reactor used for the process according to the invention. Sulfurization consists in passing a charge containing at least one sulfur compound, which once decomposed leads to the fixing of sulfur on the catalyst. This charge can be gaseous or liquid, for example hydrogen containing H ₂ S, or a liquid containing at least one sulfur-containing compound.

The interest and the advantages of the present invention are highlighted by the comparison of Example 1 according to the prior art, and Example 2, according to the invention.

Example 1 (according to the prior art):

Example 1 relates to a desulfurization process without preliminary removal of the nitrogen.

A hydrodesulfurization catalyst A is obtained by impregnating a transition alumina in the form of beads with a specific surface of 130 m2 / g and a pore volume of 1.04 ml / g, with an aqueous solution containing molybdenum and cobalt in the form of ammonium heptamolybdate and cobalt nitrate. The catalyst is then dried and calcined in air at 500 ° C. The cobalt and molybdenum content of this sample is 3% CoO and 10% MoO ₃ .

100 ml of catalyst A are placed in a tubular hydrodesulfurization reactor with a fixed bed. The catalyst is first sulfurized by treatment for 4 hours under a pressure of 3.4 MPa at 350 ° C, in contact with a load consisting of 2% sulfur in the form of dimethyldisulfide in n-heptane.

The charge treated is a catalytic cracking gasoline with an initial boiling point of 50 ° C and 225 ° C end point. Its sulfur content is 1450 ppm by weight and its index of bromine (IBr) is 69 g / 100 g. This species has a nitrogen content of 180 ppm nitrogen of which 165 ppm basic nitrogen (by basic nitrogen is understood the nitrogen included in compounds comprising a nitrogen group having a basic character). Total nitrogen is determined by the ASTM4629 method, and basic nitrogen is determined by the ASTM4739 method.

This charge is treated on catalyst A, under a pressure of 2 MPa, an H ₂ / HC ratio of 300 l / l and a VVH of 2 h ^-1 . Table 1 shows the influence of temperature on the desulfurization and saturation rates of olefins. Temperature
(° C) Sulfur content of desulphurized petrol
(ppm weight) Desulfurization rate
(HDS -%) IBr of desulphurized petrol
(g / 100 g) Olefin saturation rate
(HDO -%) 280 292 79.9 49.2 28.7 290 165 88.6 45.6 33.9 300 108 92.6 38.97 43.6

According to this example, it appears difficult to achieve for such a load of low contents sulfur in the effluents. At 300 ° C, the sulfur content of the effluent is thus greater than 100 ppm for an olefin saturation rate of almost 44%.

Example 2: according to the invention

Example 2 is carried out according to the invention, that is to say that the basic nitrogen compounds are mostly removed during an acid washing step, before the desulfurization step.

The charge treated is the same as that of Example 1. This gasoline contains 180 ppm nitrogen including 165 ppm basic nitrogen. 50 kg of this gasoline is mixed in a reactor discontinuous (or batch depending on the English termination), to 100 kg of an acid solution concentrated sulfuric acid at 10% by weight in distilled water. The mixture is stirred for 15 minutes then left to settle. The aqueous phase which is found in the lower part of the reactor is withdrawn. The remaining gasoline is washed with 50 kg of distilled water. After decantation, water is separated from gasoline.

It has been analyzed that the gasoline thus produced has a nitrogen content of 12 ppm, of which 0 ppm basic nitrogen.

The reactor used in Example 1 is charged with fresh catalyst A and sulfurized according to the same procedure as in example 1.

This charge is treated on catalyst A, under a pressure of 2 MPa, an H ₂ / HC ratio of 300 l / l and a VVH of 2 h ^-1 . The operating conditions applied for example 2 are identical to the operating conditions of example 1. Table 2 shows the influence of the temperature on the desulfurization and saturation rates of the olefins. Temperature
(° C) Sulfur content of desulphurized petrol
(ppm weight) Desulfurization rate
(HDS -%) IBr of desulphurized petrol
(g / 100 g) Olefin saturation rate
(HDO -%) 280 160 89.0 48.2 30.1 290 97 93.3 43.1 37.5 300 59 95.9 37.4 45.8

For the same operating conditions, the desulfurization rate reached by the process according to the invention is higher than that of Example 1. On the other hand, the saturation rates of the olefins are comparable. As a result, a desulfurization process carried out according to the invention allows an increase in the selectivity of the catalyst used: the losses in olefins and therefore in octane number (measured at constant desulfurization rate) are more weak when the petrol is at least partially free of nitrogen compounds before desulfurization only when treated directly.

The decrease in the nitrogen rate in gasolines before hydrodesulfurization also leads a significant improvement in the activity of the catalyst. This increase will allow example of minimizing deactivation phenomena and thus maximizing service life hydrodesulfurization catalysts by working at a lower temperature.

Claims (12)

Process for desulfurization of a petrol feed comprising at least 150 ppm by weight of sulfur-containing compounds by a hydrodesulfurization catalyst, said process being characterized in that said feed is subjected to a preliminary denitrogenation treatment under conditions such as the rate of compounds nitrogen present in said feed at the time of contact with said hydrodesulfurization catalyst does not exceed 150 ppm by weight. The method of claim 1 wherein said denitrogenation pre-treatment is carried out immediately before said contacting. Method according to claim 1, in which at least one step chosen from the group consisting of: a) the selective hydrogenation of the dienes contained in the feed, b) the transformation of the light sulfur compounds contained in the feed, c) the separation of said charge into at least two fractions, of which: a light fraction containing a minor part of the sulfur compounds, a heavy fraction containing the major part of the sulfur-containing compounds is carried out between said denitrogenation treatment (step d) and said contacting with the hydrodesulfurization catalyst (steps e and optionally f). The method of claim 3 wherein said contacting is carried out at least with the heavy fraction from step c). Method according to claim 2, in which at least one step chosen from the group consisting of: a) the selective hydrogenation of the dienes contained in the feed, b) the transformation of the light sulfur compounds contained in the feed, c) the separation of said charge into at least two fractions, of which: a light fraction containing a minor part of the sulfur compounds, a heavy fraction containing the major part of the sulfur-containing compounds is carried out before said denitrogenation treatment (step d). The method of claim 5 wherein contacting the catalyst hydrodesulfurization is carried out at least with the heavy fraction from step c). Method according to one of the preceding claims, in which said contacting is performed in at least two steps e) and f). Method according to one of the preceding claims, in which said catalyst hydrodesulfurization includes at least one element from group VIII of the classification periodic. Method according to one of the preceding claims, in which said catalyst of hydrodesulfurization includes at least one element of group VIB of the classification periodic. The method of claim 8 or 9 wherein said catalyst comprises at least one element of group VIII of the classification chosen from the group consisting of nickel and Cobalt and at least one element from group VIB of the classification chosen in the group consisting of Molybdenum and Tungsten. Method according to one of the preceding claims, in which said contacting is carried out at a temperature between 250 ° C and 350 ° C, under a pressure between 1 and 3MPa, at a liquid hourly space velocity between 1h ^-1 and 10h ^-1 and with an H ₂ / HC ratio between 50 l / l and 500 l / l. Application of the method according to one of the preceding claims to essences from catalytic cracking or coking of a heavy hydrocarbon feedstock or steam cracking.