RU2638168C2 - Method of desulfurizing gasoline - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method includes the following steps: a) conducting the demercaptization step by adding, at least, a portion of mercaptans to olefins by contacting the gasoline with, at least, the first catalyst at a temperature of 50 to 250°C, a pressure of 0.4 to 5 MPa and a liquid space velocity (LHSV) of 0.5 to 10 h^-1, wherein the first catalyst is sulphide and contains the first carrier, at least, one metal selected from group VIII, and, at least, one metal selected from group VIb of the Periodic Table of the Elements, wherein the first catalyst has the following characteristics: a carrier consisting of gamma-modification of aluminium oxide with a specific surface area of 180 to 270 m²/g, the metal content of group VIb expressed as oxide is from 4 to 20 wt % with respect to the total weight of the catalyst, the metal content of group VIII expressed as oxide is from 3 to 15 wt % with respect to the total weight of the catalyst, the molar metal ratio of Group VIII to the metal of group VIb is 0.6 to 3 mol/mol; b) fractioning the gasoline leaving step a) is carried out in the distillation column to, at least, the first intermediate light gasoline fraction with a total sulfur content that is lower than that of the original gasoline and the second intermediate heavy gasoline fraction containing most of the starting sulfur-containing compounds; c) introducing a hydrogen stream and, at least, the second intermediate heavy gasoline fraction leaving step b) to the catalytic distillation column (14) comprising, at least, one reaction zone (15), containing, at least, one second catalyst in sulfide containing the second medium, at least one metal of group VIII, and one metal of group VIb, with the metal content of group VIII expressed in the form of oxide, constituting from 0.5 to 25 wt % with respect to the weight of the catalyst, and the metal content of group VIb expressed in the form of oxide comprising from 1.5 to 60 wt % with respect to the weight of the catalyst, wherein the conditions in the catalytic distillation column are selected so that in the presence of hydrogen the intermediate heavy gasoline to be brought in contact, leaving step b), with the second catalyst for the breakdown of sulfur-containing compounds to H₂S, wherein the bringing into contact with the second catalyst is carried out under a pressure of 0.1 to 4 MPa and at a temperature of 210 up to 350°C; d) at least, one end light gasoline fraction containing H₂S and the desulfurized heavy gasoline fraction are removed from the catalytic distillation column, wherein the light end gasoline fraction is withdrawn at a point located above the reaction area, and the desulfurized heavy gasoline fraction is withdrawn at a point located below the reaction zone.

EFFECT: increasing the degree of purification.

14 cl, 4 dwg, 4 tbl, 1 ex

Description

The present invention relates to a method for the deep desulfurization of gasoline containing diolefins, olefins and sulfur compounds, including mercaptans, with minimal hydrogen consumption and preservation of the octane number.

State of the art

The production of reformulated gasolines that meet new environmental standards requires, in particular, a slight decrease in the concentration of olefins in them, but a significant decrease in the concentration of aromatic compounds (especially benzene) and sulfur. Catalytic cracking gasolines, which can make up 30 to 50% of the gasoline pool, are high in olefins and sulfur. Sulfur present in reformulated gasolines is almost 90% found in catalytic cracking gasoline (FCC, Fluid Catalytique Cracking or fluid catalytic cracking). The desulphurization (hydrodesulphurisation) of gasolines and mainly FCC gasolines is, therefore, without a doubt important to meet the technical requirements.

As a result of preliminary hydrotreatment (hydrodesulphurisation) of the feed sent to catalytic cracking, FCC gasolines are obtained, usually containing less than 100 ppm. sulfur. These hydroprocessing plants, however, operate under harsh conditions of temperature and pressure, which implies significant hydrogen consumption and high investment. In addition, all raw materials are desulfurized completely, which leads to the processing of very large volumes of raw materials.

Therefore, in order to meet the technical requirements for sulfur, there is a need for additional processing by hydrotreating (or hydrodesulfurization) of catalytic cracking gasolines. If this additional treatment is carried out under ordinary conditions familiar to the specialist, it is possible to further reduce the sulfur content in gasoline. However, the main disadvantage of this method is a significant reduction in the octane number of FCC gasolines due to the saturation of olefins during hydroprocessing.

US Pat. No. 4,131,537 teaches interest in fractionating gasoline into several fractions, preferably three, depending on their boiling point and their desulfurization under conditions that may be different, and in the presence of a catalyst containing at least one Group VIb metal and / or group VIII. This patent states that the best result is achieved if gasoline is divided into three fractions and if the fraction having intermediate boiling points is treated under mild conditions.

French patent FR 2785908 teaches interest which is the fractionation of gasoline into a light fraction and a heavy fraction followed by specific hydroprocessing of a light gasoline fraction on a nickel-based catalyst and hydroprocessing of a heavy gasoline fraction on a catalyst containing at least one Group VIII metal and / or at least one metal of group VIb.

Of the possible methods for the production of low sulfur fuel, a method has been very widely used, which consists in the specific treatment of base gasoline with a high sulfur content by hydrodesulfurization methods in the presence of hydrogen. By traditional methods, gasolines are not desulfurized selectively by hydrogenation of most olefins, which causes a significant decrease in the octane number and high hydrogen consumption. The most recent methods, such as the Prime G + method (trademark), allow desulfurization of high olefin cracking gasolines, limiting the hydrogenation of monoolefins and, consequently, lowering the octane number. Such methods are described, for example, in patent applications EP 1077247 and EP 1174485.

As indicated in patent application EP 1077247, a selective hydrogenation step of the feedstock is preferably carried out prior to the hydroprocessing stage. This first stage of hydrogenation consists mainly in the selective hydrogenation of diene compounds (diolefins), conversion by weighting of saturated light sulfur-containing compounds (by increasing their molecular weight), i.e. sulfur-containing compounds whose boiling point is lower than the boiling point of thiophene, such as methanethiol, ethanethiol, because this makes it possible then to obtain, by simple distillation and without lowering the octane number, a desulfurized light gasoline fraction consisting of a large amount of olefins.

The hydrodesulfurization step of cracking gasolines that contain monoolefins consists of a transition metal sulfide type catalyst passing through a feed to be mixed with hydrogen to convert the sulfur containing compounds to hydrogen sulfide (H ₂ S). The reaction mixture is then cooled to condense gasoline. The gaseous phase containing an excess of hydrogen and H ₂ S is separated and the desulphurized gasoline is recovered.

Residual sulfur-containing compounds, mainly present in desulphurized gasoline, can be divided into two different groups: non-hydrogenated sulfur-containing compounds present in the feed, on the one hand, and sulfur-containing compounds formed in the reactor as a result of secondary reactions called recombination reactions. In this latter group of sulfur-containing compounds, the more numerous compounds are mercaptans obtained by adding H ₂ S formed in the reactor to the monoolefins present in the feed. Mercaptans having the chemical formula R-SH, where R is an alkyl group, are also called recombinant mercaptans and they comprise mainly 20% of the mass. up to 80% of the mass. residual sulfur in desulfurized gasoline.

The selective hydrogenation step described in patent application EP 1077247 is necessary in order to prevent the gradual deactivation of the selective hydrodesulfurization catalyst, to avoid the gradual contamination of the reactor with polymer resin formed on the surface of the catalysts or in the reactor, and the heat exchangers becoming too contaminated. Saturation of diolefins is mainly not necessary for the end use of sulfur-free gasoline. The disadvantage of this stage of selective hydrogenation, necessary only for the good functioning of the method in patent application EP 1077247, is the excessively high hydrogen consumption associated with the saturation of the raw material diolefins. Since hydrogenation of diolefins is carried out under harsh conditions, it is mainly accompanied by a low degree of hydrogenation of olefins, which further increases the consumption of hydrogen and leads to a decrease in the octane number. Finally, in addition to the hydrogen used, hydrogen is also lost at the beginning of the distillation between the selective hydrogenation step and the hydrodesulfurization step of the process in patent application EP 1077247 to the extent that an excess of hydrogen is required mainly for the conversion of almost all diolefins in the first stage.

Also known patent US 6984312, which discloses a method for processing light gasoline catalytic cracking (C5-175 ° C) containing olefins, diolefins, mercaptans and heavy sulfur-containing organic compounds. The method includes a first thioesterification step in which mercaptans are reacted with raw diolefins in the presence of a thioesterification catalyst to produce sulfides. The gasoline subjected to this first stage is then sent to a distillation column, where it is fractionated into a light fraction depleted in sulfur, and a heavy fraction containing sulfides formed in the first stage, as well as heavy sulfur-containing organic compounds originally present in the gasoline to be treated. The heavy fraction is then treated in the presence of hydrogen and heavy naphtha cracked in the reactive distillation zone containing the hydrodesulfurization catalyst. Cracked heavy naphtha is returned to the reactive distillation zone so that the distillation column can operate at a high temperature while maintaining the liquid fraction in the catalyst bed.

By the method described in US Pat. No. 6,984,312, it is difficult to obtain a light gasoline fraction that meets future technical requirements for sulfur content, i.e. with an upper limit to the total sulfur content of gasoline of 50 ppm (mass.), even 30 or 10 ppm mass (without additional processing of this light fraction). Indeed, the removal of mercaptans occurs by adding to the diolefins contained in the feed, a nickel or palladium-based thioesterification catalyst. Therefore, a catalyst of this type also catalyzes the selective hydrogenation of diolefins. Thus, both reactions compete for diolefins and, as a result, there is limited conversion of mercaptans by thioesterification. The light gasoline obtained at the top of the distillation column by the method described in US Pat. No. 6,984,312 may therefore contain a significant fraction of the light mercaptans present in the feedstock. Therefore, additional processing of the light fraction by hydrodesulfurization is necessary to reduce the sulfur content in the light fraction of gasoline.

The disadvantage of the method described in patent US 6984312, is that they process only light gasoline, and not all gasoline as a whole. It was found that total gasoline (the boiling point of which is mainly from 20 ° C to 230 ° C) cannot be effectively processed in the thioesterification reactor due to the high sulfur content, which is poison for thioesterification catalysts, in particular, nickel-based catalysts (see patent US 7638041) or based on palladium (see patent US 5595634).

The aim of the invention, therefore, is a method for producing gasoline from a broad gasoline spectrum with a low sulfur content, i.e. a sulfur content of less than 50 ppm mass., preferably less than 30 ppm or 10 ppm mass., while limiting the consumption of hydrogen and lower octane number.

A brief description of the invention.

To this end, a method is proposed for treating gasoline containing diolefins, oleins and sulfur-containing compounds, including mercaptans, the method comprising the following steps:

a) carry out the stage of demercaptization by attaching at least part of the mercaptans to olefins by bringing gasoline into contact with at least the first catalyst at a temperature of from 50 to 250 ° C, pressure from 0.4 to 5 MPa and LVVH from 0.5 to 10 hour ^-1 , while the first catalyst is a sulfide and contains a first support, at least one metal selected from group VIII, and at least one metal selected from group VIb of the periodic table of elements, mass percentage, expressed in equivalent metal oxide selected from gro pp VIII, with respect to the total weight of the catalyst, is from 1 to 30% and the weight percent, expressed as the equivalent of a metal oxide selected from group VIb, is from 1 to 30% with respect to the total weight of the catalyst;

b) fractionation of gasoline leaving step a) is carried out in a distillation column to at least a first intermediate light gasoline fraction with a total sulfur content that is lower than that of the original gasoline, and a second intermediate heavy gasoline fraction containing most of the initial sulfur-containing compounds ;

c) introducing a hydrogen stream and at least a second intermediate heavy gasoline fraction leaving step b) into a catalytic distillation column including at least one reaction zone containing at least one second sulfide catalyst containing a second support at least one metal of group VIII and at least one metal of group VIb, and the conditions in the catalytic distillation column are selected so that in the presence of hydrogen to bring into contact the intermediate heavy gasoline, leaving s from step b), with a second catalyst for the cleavage of sulfur-containing compounds to H ₂ S,

d) at least one final light gasoline fraction containing H ₂ S and a desulfurized heavy gasoline fraction are withdrawn from the catalytic distillation column, the final light gasoline fraction is withdrawn at a point located above the reaction zone, and the sulfur-rich heavy gasoline fraction is withdrawn at a point located under the reaction zone.

The method of the invention comprises a first step a) in which sulfur-containing compounds such as mercaptan (R-SH) are converted into heavier sulfur-containing compounds by reacting with olefins present in the gasoline being processed. The demercaptization reactions of the invention are distinguished by the removal of mercaptans using olefins:

- either by direct attachment to a double bond to obtain sulfides with a higher boiling point,

either by hydrolysis: the hydrogen present in the reactor leads to the formation of H ₂ S by contact with mercaptan, which attaches directly to the olefin double bond to form a heavier mercaptan, i.e. with a higher boiling point. This route, however, is rarer under the preferred reaction conditions.

At this first stage of weighting the mercaptans achieve a very high degree of conversion (> 90% and very often> 95%), because Demercaptization reactions are carried out selectively using olefins, which are mainly present in large quantities. The lightest mercaptans are the most reactive at this stage a).

In addition, H ₂ S, if present in the feed, is converted to mercaptan (which can also be converted) by addition to olefins using a catalyst under the chosen conditions. This avoids the presence of H ₂ S in the gases in the upper part in stage b), which contain a lot of hydrogen that has not come into contact in stage a), which should be recycled to stage a). This recirculation, made possible by the absence of H ₂ S in these gases, further reduces hydrogen consumption in step a), which is an advantage of the process of the invention.

The demercapization reactions are preferably carried out on a catalyst containing at least one group VIII metal (groups 8, 9 and 10 of the new periodic classification Handbook of Chemistry and Physics, 76th edition, 1995-1996) and at least one group VIb metal (group 6 of the new Periodic Classification Handbook of Chemistry and Physics, 76th edition, 1995-1996) and carrier.

Before contacting the raw material to be treated, the catalyst goes through a sulfonation step. The catalyst participates in the targeted demercapization reactions only in the form of sulfide. Sulfonation is preferably carried out in a sulfate reducing medium, i.e. in the presence of H ₂ S and hydrogen to convert metal oxides to sulfides, such as, for example, MoS ₂ and Ni ₃ S ₂ .

According to the invention, the method includes a step b) of fractionating the stream exiting from a) of the demercaptization stage, which is carried out in a fractionation column (or splitter). The column configuration ensures the separation of gasoline into at least two fractions, namely: an intermediate light gasoline fraction with a total sulfur content that is less than that of the original gasoline, and an intermediate heavy gasoline fraction containing most of the initial sulfur-containing compounds, as well as sulfur-containing products, formed in stage a). The distillation column in step b) may also function as a depentanizer or dehexanizer. Preferably, the separation point of the distillation column in step b) is selected so that thiophene does not enter the intermediate light gasoline fraction. Sulfur-containing compounds with a lower boiling point than the boiling point of thiophene (i.e. 84 ° C) are converted in stage a) of demercaptinization and therefore they are transferred to an intermediate heavy fraction, a combination of stages a) and b) allows to obtain an intermediate light gasoline very low sulfur fraction.

The intermediate light gasoline fraction has a sulfur content of less than 50 ppm. mass., preferably less than 30 ppm, even less than 10 ppm and contains at least a combination of olefins C5, preferably compounds C5 and at least 20% of the mass. olefins C6. The extraction of most of the olefins from raw materials in the intermediate light gasoline fraction can significantly improve the selectivity of the method with respect to the hydrogenation of olefins and avoid excessive consumption of hydrogen, because olefins are not sent back to the selective hydrodesulfurization section and therefore will not be hydrogenated.

The intermediate heavy gasoline fraction contains mainly hydrocarbons with a boiling point, for example, above 84 ° C, heavy sulfur-containing compounds (from the group of thiophenes, sulfides, disulfides) that were originally present in the gasoline to be treated, as well as sulfur-containing compounds, mainly of the type of sulfides, which formed during stage a) by adding mercaptans to olefins.

According to the invention, the method includes a step c) of hydrodesulfurization of the heavy fraction leaving the fractionation step b). This treatment is carried out in a distillation column in which there is a catalytic reaction zone, also called a “catalytic column”.

This step c) consists in desulphurizing the feed of the catalyst column by contacting with hydrogen injected into the column and a hydrodesulfurization catalyst.

The distillation column is configured to operate under operating conditions that allow sulfur-containing raw material compounds (mercaptans, sulfides and thiophene compounds) to be reacted with hydrogen to form H ₂ S.

Simultaneously with step c), step d) takes place in the catalytic distillation column, in which the feedstock consisting of at least a second intermediate heavy fraction leaving the fractionation step b) is separated, possibly mixed with a recycle stream, into at least two fractions, namely, the final desulfurized light gasoline fraction obtained by decomposition of sulfur-containing compounds, and desulfurized heavy fraction.

The final desulfurized light gasoline fraction is removed from the upper part of the catalytic column with H ₂ S obtained by desulfurization and hydrogen that has not come into contact, while the desulfurized heavy fraction is withdrawn mainly from the lower part, even from the bottom of the catalytic column.

Alternatively, the additional desulfurized gasoline fraction can be recovered as a side distillation at a point located between the feed point and the bottom of the column.

The final desulphurized light gasoline fraction, followed by H ₂ S and hydrogen not reacted in the catalyst column, is then condensed to separate non-condensable compounds from the liquid phase. Part of this final light gasoline fraction is removed, and another part is returned to the column as internal reflux.

Alternatively, the method of the invention also includes the step of recirculating all or part of the desulfurized heavy gasoline fraction to a catalytic distillation column. When using possible recirculation, it is also possible to carry out an additional supply and purification of the recirculation stream.

According to an embodiment in which the recirculation of the desulfurized heavy gasoline fraction is complete and no further recovery occurs, the fractionation carried out in the catalyst column serves only to ensure recirculation of the desulfurized heavy gasoline fraction. In this case, the final light gasoline fraction recovered from the top of the catalytic distillation column consists of a second intermediate heavy gasoline fraction leaving step b). The desulfurized heavy fraction, which is removed from the bottom of the column, in this case consists of a hydrocarbon fraction introduced at an additional charge, with a boiling point in a higher temperature range than the second intermediate heavy fraction leaving step b). This external hydrocarbon fraction, which is then recirculated to the catalytic distillation column, serves to maintain the liquid phase at the bottom of the catalytic column, allowing the column to operate at a higher temperature to desulfurize the heaviest sulfur-containing molecules that are most difficult to convert. The bottom of the catalytic column operating at high temperature is the zone of the catalytic layer most sensitive to decontamination as a result of the deposition of coke or resins. This heavier fraction is preferably a paraffin type fraction and serves as a solvent for washing off coke and resins that are deposited on the bottom of the catalyst column. This flushing is necessary to obtain a long life cycle of the catalytic layer. This is all the more correct since the feed in the catalyst column contains a large number of unsaturated compounds such as diolefins.

This embodiment is advantageous for limiting hydrogen consumption in step a), because a hydrogenation step for the resin and coke precursors (in particular compounds such as diolefins) is not necessary.

According to another embodiment, in which no recirculation of the desulfurized heavy gasoline fraction occurs, the intermediate heavy gasoline fraction leaving the fractionation step b) is separated into at least two fractions, each of which fractions is desulfurized. With this configuration, both fractions recovered at the outlet of the catalyst column are used directly in the gasoline pool.

According to another embodiment, the catalytic distillation column is configured to separate the second intermediate heavy gasoline fraction leaving the fractionation step b) into at least two desulfurized fractions. In this embodiment, moreover, an additional supply of an external fraction of heavy hydrocarbons occurs. These additionally introduced hydrocarbons are recycled to the catalytic distillation column to maintain the liquid phase at the bottom of the catalyst column. In this case, both desulfurized fractions originating from the second intermediate heavy gasoline fraction are removed respectively from the upper part of the column (final light fraction) and by side distillation (additional desulfurized gasoline fraction), and the desulfurized heavy fraction which is removed from the bottom of the column is recirculating heavy fraction. Partial recycling can also be carried out within the scope of the invention.

An advantage of the method according to the invention is that there is no need to desulfurize the light gasoline fraction leaving the fractionation step b), because almost all sulfur-containing compounds of the mercaptan type were converted in stage a) to compounds with a higher molecular weight, so that they turned into a heavy gasoline fraction. This gasoline fraction has a low sulfur content and a good octane rating and does not require further processing.

In step a), hydrogenation reactions are not required. Hydrogen, if used, serves primarily to preserve the hydrogenating surface of the catalyst, providing a high yield of demercaptization reactions. Thus, low pressure does not adversely affect the method of the invention and the consumption of hydrogen is low, which is an advantage of the method of the invention.

Another advantage of the method according to the invention is that both first stages can be carried out at the same pressure (except for the loss of raw materials), because stage a) requires a small amount of hydrogen, even does not require at all, as well as stage b). The absence of the need for a diene removal reaction in step a) is also favorable with respect to hydrogen consumption, since at this stage, hydrogen is not consumed or is consumed in very small quantities. Such operation during exhaustion in stages a) and b) allows the gas to be returned from the upper part of the column in stage b) with a high hydrogen content to the demercaptization reactor in stage a), if in stage a) the catalyst must have a hydrogenation surface suitable for a high degree of conversion with demercaptization. This recirculation reduces the hydrogen consumption in step a) and avoids the loss of this hydrogen in the gaseous fuel supply system. This hydrogen usually does not contain H ₂ S, because the latter is not produced by the catalyst used in step a) under the selected conditions. This H ₂ S can even be converted in step a) if present in the feed.

An advantage of the process of the invention is that the catalyst and operating conditions used in step a) allow, in contrast to thioesterification reactors, such as those described in the prior art, to process all gasoline (i.e., C5-220 ° C.) with a high content sulfur. The treatment of the entire gasoline fraction with a catalyst is especially preferred for maintaining the liquid phase in step c) if a high degree of conversion during desulfurization is required, i.e. if the catalytic column is operating at high temperature.

The use of a catalytic column, rather than a conventional hydrodesulfurization reactor in a fixed bed, allows continuous irrigation of the catalytic zone with countercurrent liquid inside the column. This irrigation of the catalytic zone also allows washing away the resins that may form during the polymerization of diolefins. The partial pressure of hydrogen is also lower than traditional hydrodesulfurization in a fixed bed, which helps to avoid undesirable hydrogenation reactions of olefins, which cause both excessive hydrogen consumption and a decrease in octane number.

Another advantage associated with the use of a catalytic column for selective hydrodesulfurization is that a continuous downward flow of hydrogen moves the H ₂ S generated during the hydrodesulfurization reactions and thus helps to limit the formation of recombinant mercaptans by adding hydrogen sulfide to the remaining olefins.

DETAILED DESCRIPTION OF THE INVENTION

The object of the present invention is a method for the desulfurization of gasoline with a limited sulfur content, starting from gasoline, preferably originating from a catalytic cracking unit, coking unit or a unit for reducing viscosity. Gasoline can be gasoline of the so-called full cracking (C5-220 ° C) or gasoline, the final boiling point of which is lower than or equal to 210 ° C (light gasoline).

According to the invention, gasoline is first subjected to step a) the conversion of sulfur-containing compounds, mainly mercaptans, the lightest gasoline compounds, using olefins to increase their molecular weight. The method also includes a second stage b), which consists in moving all or part of the gasoline from stage a) to a fraction column, also called a “splitter”.

Such a sequence of operations allows to obtain a light fraction, the sulfur content of which is reduced without a significant reduction in the olefin content and with a high degree of hydrodesulfurization, as well as without the need for processing of this light gasoline in an additional section of hydrodesulfurization or using methods to restore the octane number of gasoline.

The method according to the invention allows, therefore, to obtain a light gasoline fraction, which can be sent directly to the pool of gasoline, the total sulfur content of which is less than 50 ppm, preferably less than 30 ppm, even less than 10 ppm. depending on the amount of sulfur initially present and the chemical nature of the sulfur-containing compounds.

The method according to the invention also comprises a step c) of hydrodesulfurization of the heavy fraction originating from fractionation step b). This treatment is carried out in a distillation column in which there is a catalytic reaction zone, also called a “catalytic column”.

This second stage consists in the desulfurization of this first heavy fraction by contacting with hydrogen on a catalytic layer.

The catalytic distillation column is configured for operation under operating conditions that allow:

- enter into the interaction of sulfur-containing compounds of raw materials (mercaptans, sulfides and thiophene compounds) with hydrogen with the formation of H ₂ S,

- to separate raw materials containing at least an intermediate heavy gasoline fraction originating from fractionation step b) into at least two fractions, namely, the final light gasoline fraction depleted in sulfur-containing compounds to a very low sulfur content and containing most of the olefins, and heavy a desulfurized fraction, also low in sulfur.

As used herein, the term “catalytic column” means a device in which a catalytic reaction and separation of products occur at least simultaneously. The device used may include a distillation column equipped with a catalytic section in which the catalytic reaction and distillation occur simultaneously. It can also be a distillation column in combination with at least one reactor located inside the column and on the wall of the latter. The internal reactor may function as a vapor phase reactor, or as a liquid phase reactor with liquid / vapor circulation in one direction or countercurrent.

The advantage of using a catalytic distillation column compared to a reactor with a single fixed bed operating in the gaseous phase is the ability to continuously irrigate the catalytic zone with countercurrent liquid inside the column. This irrigation of the catalytic zone allows to reduce the coking of the catalyst and, thus, to extend the cycle of the catalyst for hydrodesulfurization. The partial pressure of hydrogen is also reduced in comparison with traditional hydrodesulfurization in a fixed bed, which helps to avoid undesirable hydrogenation reactions of olefins, which simultaneously lead to excessive hydrogen consumption and lower octane number. The use of a catalytic column also allows you to control the reaction, facilitating the exchange of heat generated; the heat released during the reaction can be absorbed by heat to evaporate the mixture.

Gasoline to be processed.

The method according to the invention allows to process any type of gasoline fraction containing sulfur, preferably a gasoline fraction originating from a catalytic cracking unit, the boiling point of which is usually from about the boiling point of hydrocarbons containing 2 or 3 carbon atoms (C2 or C3), to 250 ° C, more preferably from about the boiling point of hydrocarbons containing 5 carbon atoms, to about 220 ° C.

The method according to the invention also applies to a gasoline fraction previously stabilized, i.e. gasoline fraction from which hydrocarbons containing less than 6 or 5 carbon atoms are removed.

The method according to the invention can also process gasoline raw materials, called "light", with a final boiling point below the above, which, for example, is lower than or equal to 210 ° C, lower or equal to 180 ° C, lower or equal to 160 ° C or lower or equal 145 ° C.

The sulfur content of gasoline fractions obtained by catalytic cracking (FCC) depends on the sulfur content of the FCC-treated feedstock, the presence or absence of pre-treatment of FCC feedstock, and the final boiling point of the fraction. Mostly, the sulfur content in the whole gasoline fraction, in particular, derived from FCC, is greater than or equal to 100 ppm. mass and mainly more than 500 ppm mass In gasolines whose final boiling point exceeds 200 ° C, the sulfur content is often greater than 1000 ppm. mass., in some cases, it can even reach values of the order of 4000-5000 ppm mass

For example, gasolines originating from catalytic cracking units (FCC) contain on average from 0.5% to 5% of the mass. diolefins, from 20% to 50% of the mass. olefins, from 10 ppm up to 0.5% of the mass. sulfur, from which mercaptans are mainly less than 300 ppm. Mercaptans are mainly concentrated in light fractions of gasoline and more specifically in a fraction whose boiling point is below 120 ° C.

It should be noted that the sulfur-containing compounds present in gasoline may also contain heterocyclic sulfur-containing compounds, such as, for example, thiophenes, alkylthiophenes or benzothiophenes.

Stage a) weighting mercaptans with olefins

This stage consists in the conversion of light sulfur-containing compounds from the group of mercaptans, i.e. compounds that would be contained in light gasoline at the exit from stage b) of fractionation into heavier sulfur-containing compounds which are transferred to the intermediate heavy gasoline fraction in stage b) of fractionation.

At this stage a), a demercaptization reaction occurs during which mercaptans join the olefins of the feed in the presence of a catalyst.

Typically, mercaptans that can interact in step a) are as follows (the list is not exhaustive): methyl mercaptan, ethyl mercaptan, n-propyl mercaptan, isopropyl mercaptan, tert-butyl mercaptan, n-butyl mercaptan, sec-butyl mercaptan, methyl-mercaptan, isl-mercaptan, i-mercaptan, α-ethylpropyl mercaptan, n-hexyl mercaptan, 2-mercaptohexane.

The demercaptization reaction is preferably carried out on a catalyst containing at least one metal of group VIII (groups 8, 9 and 10 of the new periodic classification Handbook of Chemistry and Physics, 76th edition, 1995-1996), at least one metal of group VIb (group 6 of the new Periodic Classification Handbook of Chemistry and Physics, 76th edition, 1995-1996) and carrier. The Group VIII metal is preferably selected from nickel and cobalt, and in particular from nickel. The metal of group VIb is preferably selected from molybdenum and tungsten, and very preferably from molybdenum.

The catalyst carrier is preferably selected from alumina, nickel aluminate, silicon oxide, silicon carbide, or a mixture of these oxides. Preferably, alumina is used, and more preferably pure alumina. Preferably, a support is used with a total porosity measured by mercury porosimetry of 0.4 to 1.4 cm ³ / g and preferably 0.5 to 1.3 cm ³ / g. The specific surface area of the carrier is preferably from 70 m ² / g to 350 m ² / g. In a preferred embodiment, the support is a cubic gamma modification of alumina or a delta modification of alumina.

The catalyst used in stage a) mainly contains:

- a carrier consisting of a gamma or delta modification of alumina with a specific surface area of 70 m ² / g to 350 m ² / g.

- the mass content of the metal oxide of group VIb is from 1 to 30% of the mass. in relation to the total weight of the catalyst,

- the mass content of the metal oxide of group VIII is from 1 to 30% of the mass. in relation to the total weight of the catalyst,

- the degree of sulfonation of the metals that make up the specified catalyst is at least 60%,

- the molar ratio of the base metal of group VIII and the metal of group VIb is from 0.6 to 3 mol / mol.

In particular, it was found that the technical properties of the catalysts are improved if the catalyst has the following characteristics:

- a carrier consisting of a gamma modification of alumina with a specific surface area of 180 m ² / g to 270 m ² / g,

- the mass content of the metal oxide of group VIb, expressed in the form of oxide, is from 4 to 20% by weight relative to the total weight of the catalyst, preferably from 6 to 18% by weight,

- the mass content of the metal oxide of group VIII, expressed in the form of oxide, is from 3 to 15% of the mass. and preferably from 4 to 12% of the mass. in relation to the total weight of the catalyst,

- the molar ratio of the base metal of group VIII and the metal of group VIb is from 0.6 to 3 mol / mol and preferably from 1 to 2.5 mol / mol.

In a preferred embodiment, the catalyst is used with a mass content of nickel oxide (in the form of NiO), of from 4 to 12 wt.%, With the weight content of molybdenum oxide (MoO ₃ in the form) of _from 6 to 18% by weight. and a mass ratio of nickel / molybdenum, comprising from 1 to 2.5, while the metals are deposited on a carrier consisting only of aluminum oxide, and the degree of sulfonation of the metals included in the catalyst exceeds 80%.

The catalyst according to the invention can be obtained by any technology known to a person skilled in the art, and in particular by impregnation of the selected support with metals of groups VIII and VIb.

After the introduction of metals of groups VIII and VIb and possibly molding the catalyst, it is subjected to activation. The purpose of this treatment is mainly to convert the molecular precursors of metals to the oxide phase. In this case, we are talking about oxidative treatment, but you can also just carry out the drying of the catalyst. In the case of an oxidative treatment, also called calcination, the catalyst is mainly treated in air or in an atmosphere of diluted oxygen and the treatment temperature is mainly from 200 ° C to 550 ° C, preferably from 300 ° C to 500 ° C.

After calcination, the metals deposited on the carrier are in the form of oxides. In the case of nickel and molybdenum, the metals are mainly in the form of MoO ₃ or NiO. Before being brought into contact with the processed feed, the catalysts go through a sulfonation step. Sulfonation is preferably carried out in a sulfate reducing medium, i.e. in the presence of H ₂ S and hydrogen to convert metal oxides to sulfides, such as for example MoS ₂ and Ni ₃ S ₂ . Sulfonation is carried out by feeding to the catalyst a stream containing H ₂ S and hydrogen, or a sulfur-containing compound capable of decomposing to H ₂ S in the presence of a catalyst and hydrogen. Polysulfides such as dimethyldisulfide are H ₂ S precursors widely used for sulfonation of catalysts. The temperature is set so that H ₂ S interacts with metal oxides to form metal sulfides. This sulfonation can be carried out in situ or ex situ (inside the reactor or outside the reactor) of the demercaptization reactor at a temperature of from 200 to 600 ° C and more preferably from 300 to 500 ° C.

Stage a) can be carried out without adding hydrogen to the reactor, but preferably hydrogen is injected with the feed to maintain the hydrogenation ability of the catalyst surface for a high degree of conversion during demercaptization. Typically, step a) is carried out at a H ₂ / feed ratio of 0 to 25 Nm ^{3 of} hydrogen per m ^{3 of} feed, preferably 0 to 10 Nm ^of hydrogen per m ^{3 of} feed, very preferably 0 to 5 Nm ^of hydrogen per m ^{3 of} raw materials and more preferably from 0.5 to 2 Nm ^{3 of} hydrogen per m ^{3 of} raw materials.

The total amount of feed is usually introduced through the inlet of the reactor. However, in some cases, it is preferable to introduce part or all of the feed between two successive catalytic layers in the reactor. This embodiment allows, in particular, to continue the operation of the reactor if the entrance to the reactor is clogged with deposits of polymers, particles or resins present in the feed.

The gasoline to be treated is brought into contact with the catalyst at a temperature of from 50 ° C to 250 ° C, preferably from 80 ° C to 220 ° C, and even more preferably from 90 ° C to 200 ° C, with a volumetric fluid velocity (LHVS) of from 0.5 h ^-1 to 10 h ^-1 , and the unit volumetric velocity of the liquid is a liter of feed per liter of catalyst per hour (l / l /h). The pressure is from 0.4 MPa to 5 MPa, and preferably from 0.6 to 2 MPa, and more preferably from 0.6 to 1 MPa.

At the end of stage a), the content of mercaptans in gasoline processed under the conditions described above is reduced. Mostly produced gasoline contains less than 50 ppm. mass mercaptans and preferably less than 10 ppm mass Light sulfur-containing compounds, the boiling point of which is lower than the boiling point of thiophene (84 ° C), mainly turn more than 80%, even more than 90%. Olefins are not hydrogenated or hydrogenated to a very small extent, which allows to maintain a good octane number at the exit from stage a). The degree of hydrogenation of olefins is typically less than 2%.

Stage b) separation of the intermediate light gasoline fraction and the intermediate heavy gasoline fraction

Stage b) of the separation is preferably carried out in a conventional distillation column, also called a “splitter”. This fractional column allows the separation of the intermediate light gasoline fraction with a low content of sulfur-containing compounds and the intermediate heavy gasoline fraction, preferably containing most of the sulfur-containing compounds originally present in the starting gasoline.

This fractional column operates mainly at a pressure of from 0.1 to 2 MPa and preferably from 0.6 to 1 MPa. It should be noted that this pressure can essentially be the same (with the exception of the loss of raw materials) as the pressure in the reactor in stage a). Such operation during exhaustion in stages a) and b) allows gas to be returned from the upper part of the column of stage b) with a high hydrogen content to the demercaptization reactor in stage a) (if in stage a) the catalyst must have a hydrogenation surface suitable for a high degree of conversion at demercaptization). This recirculation reduces the hydrogen consumption in step a) and avoids the loss of this hydrogen in the gaseous fuel supply system. This hydrogen usually does not contain H ₂ S, because the latter is not produced by the catalyst used in step a) under the selected conditions.

The number of theoretical plates in this separation column is usually from 10 to 100, preferably from 20 to 60. The reflux ratio obtained by dividing the liquid flow rate in the column by the distillate flow rate, expressed in kg / h, is mainly less than one and preferably less than 0.8.

The intermediate light gasoline obtained by separation b) contains mainly at least a combination of C5 olefins, preferably C5 compounds and at least 20% C6 olefins. The column fractionation temperature is often set so that thiophene does not move into the intermediate light gasoline fraction. Thus, the initial temperature of the distillation range of the intermediate heavy gasoline fraction is about 84 ° C. This initial temperature is possibly higher depending on the expected sulfur content in the intermediate light gasoline fraction and can be about 100 ° C, even up to 120 ° C.

Alternatively, the distillation column is configured to allow lateral extraction of the intermediate gasoline fraction, i.e. gasoline fraction, the boiling point of which is between the final boiling point of the intermediate light gasoline fraction and the initial boiling point of the intermediate heavy gasoline fraction. The specified intermediate gasoline fraction can then be subjected to hydrodesulfurization in a dedicated reactor and then mixed with the intermediate light gasoline fraction.

Stage c) and d) hydrodesulfurization in a catalytic column.

The desulfurization reaction in step c) is a hydrodesulfurization reaction, which involves passing a feed in the presence of hydrogen, which is injected into said column of at least one catalyst at least partially in the form of a sulfide containing at least one metal of group VIII, according to at least one metal of group VIb and possibly phosphorus, at a temperature of from 210 ° C to 350 ° C, preferably from 220 ° C to 320 ° C. The pressure at the top of the column is mainly maintained between about 0.1 and about 4 MPa, and preferably between 1 and 3 MPa. The ratio of consumption of N ₂ / consumption of raw materials in the column is from 25 to 400 Nm ³ per m ^{3 of} liquid raw materials and preferably from 40 to 100 Nm ³ per m ^{3 of} liquid raw materials.

The Group VIII metal is preferably cobalt or nickel, and the Group VIb metal is mainly molybdenum or tungsten. Preferred are cobalt-molybdenum and nickel-molybdenum combinations. The content of the metal of group VIII, expressed by oxide, is mainly from 0.5 to 25 wt. -%, preferably from 1 to 10% of the mass. in relation to the weight of the catalyst. The metal content of group VIb, expressed by oxide, is mainly from 1.5 to 60% by weight, preferably from 3 to 50% by weight. in relation to the weight of the catalyst.

Preferably, if the catalyst is of the cobalt-molybdenum type, the cobalt content expressed by the oxide is mainly from 0.5 to 15% by weight. and more preferably from 2 to 5% by weight, the molybdenum content expressed by the oxide is from 1.5 to 60% by weight. and more preferably from 5 to 20% of the mass.

Preferably, if the catalyst is of the nickel-molybdenum type, the nickel content expressed by the oxide is mainly from 0.5 to 25% of the mass. and more preferably from 5 to 25% by weight, the molybdenum content expressed by the oxide is from 1.5 to 30% by weight. and more preferably from 3 to 20% of the mass.

The catalyst carrier is usually a solid porous substance, such as, for example, alumina, silica-alumina or other solid porous substances, such as, for example, magnesium oxide, silica or titanium oxide, individually or in admixture with alumina or silica-alumina and may initially be in the form of extruded elements of small diameter or spheres. In the column, the catalyst must have a structure adapted for catalytic distillation in order to simultaneously act as a catalytic agent for carrying out the reactions, as well as as a mass transfer agent, so as to provide accessible separation layers along the layer.

To minimize the hydrogenation of olefins in the processed feed, it is preferable to use a cobalt-molybdenum type catalyst in which the molybdenum density, expressed in% by weight. MoO ₃ per unit surface is greater than 0.07 and preferably greater than 0.12. The catalyst of the invention preferably has a specific surface area of less than 250 m ² / g, more preferably less than 230 m ² / g, and very preferably less than 190 m ² / g.

In order to achieve a high degree of conversion during hydrodesulfurization and at the same time during the hydrogenation of olefins (in particular, at the bottom of the catalyst column during heavy gasoline fraction recycling), it is preferable to use a nickel-molybdenum catalyst. The catalyst of the invention in these cases preferably has a specific surface area of 70 to 250 m ² / g.

The application of metals to the support is carried out by any methods known to the skilled person, such as, for example, dry impregnation with an excess of a solution containing metal precursors. The specified solution is chosen so as to dissolve the metal precursors in the required concentrations. In the case of the synthesis of a CoMo catalyst, for example, the molybdenum precursor may be molybdenum oxide, ammonium heptomolybdate. With respect to cobalt, for example, cobalt nitrate, cobalt hydroxide, cobalt carbonate can be called. The precursors are mainly dissolved in a medium providing for their dissolution in the required concentrations. Thus, in different cases, an aqueous and / or organic medium is used as a solvent. Phosphorus can be added as phosphoric acid.

Within the framework of the invention, more than one catalytic layer can be used in the reaction zone, for example, two different catalytic layers separated by space. In some configurations, the catalyst column may also contain more than one catalyst layer containing different catalysts, in particular if it is desired to use an effective combination of different properties of cobalt-molybdenum and nickel-molybdenum catalysts. In another configuration, in the method according to the invention, the catalytic layer of the column can be only above or only below the place of input of raw materials.

When the catalyst column is operating in the reaction zone, steam and liquid are simultaneously formed. A significant part of the vapor is hydrogen, the rest consists of a part of the evaporated raw materials and hydrogen sulfide.

As with any distillation, a temperature gradient exists in the system so that compounds with a higher boiling point are found in the lower part of the column than in the upper part of the column. Distillation allows the separation of compounds present in the feed due to the difference in boiling point.

The reaction heat, possibly generated in the catalytic column, is removed by evaporation of the mixture on the distillation plate in question. Therefore, the temperature profile of the column is very stable and the catalytic reactions that occur on the layer do not interfere with its operation. Also, this stability of the temperature profile allows one to obtain stable reaction kinetics, since they are isothermal on each dividing tier, while temperatures depend only on the liquid-vapor equilibrium of the dividing tiers and pressure regulation in the column.

The catalytic distillation column is configured to operate under operating conditions that allow separation of the feedstock consisting of at least a second intermediate heavy fraction originating from fractionation step b) into at least two fractions, namely a desulfurized final light gasoline fraction obtained decomposition of sulfur-containing compounds, and desulfurized heavy fraction.

The final light gasoline fraction is recovered in the upper part of the catalytic column with H ₂ S formed during desulfurization and unreacted hydrogen, while the desulfurized heavy gasoline fraction is recovered from the bottom of the catalyst column.

In an embodiment, the additional desulfurized gasoline fraction can be recovered by lateral sampling at a point located between the feed inlet and the bottom of the column.

Preferably, the final light gasoline fraction, followed by H ₂ S formed during the desulfurization reactions and not reacted with hydrogen, is cooled to a temperature, mainly below 60 ° C, to condense the hydrocarbons. The gaseous phases (containing mainly the formed H ₂ S and unreacted hydrogen) and the liquid hydrocarbon phase (i.e. the final light gasoline fraction suitable for processing) are separated in a separator. A portion of this final light gasoline fraction is transferred to a gasoline pool, while another portion is recycled to the column as internal reflux. Internal reflux is at the same time suitable for distillation of the feed and also allows continuous flushing of the catalyst. The downward flow of liquid in the column allows you to clean the catalyst from coke and resins, which can be formed in particular as a result of the presence of highly unsaturated compounds in the feed, diolefin or acetylene type. This allows to reduce the deactivation of the catalyst and, therefore, to ensure a long cycle.

The gaseous phase rich in H ₂ S and hydrogen can be sent, for example, to an amine-containing absorber for purification and extraction of hydrogen for reuse in the process.

In an embodiment, the method of the invention also includes the step of recirculating in the catalytic column all or part of the desulfurized heavy gasoline fraction, which is taken from the bottom of said catalytic column. If you use this possible recirculation, you can also perform additional loading and clean the recirculation stream.

Alternatively, the recycle stream may also contain an external hydrocarbon fraction (supplied with additional charge), the initial boiling point of which is higher than or equal to the boiling point of the intermediate heavy gasoline fraction. This external hydrocarbon fraction is withdrawn from the bottom of the catalytic distillation column and returned along the circuit to said column.

Various options for the method according to the invention are given below, and the list of these options is not exhaustive.

In a first embodiment, the feed to Step c) consisting of an intermediate heavy gasoline fraction originating from Step b) is separated into at least two gasoline fractions. In this embodiment, the final light gasoline fraction and desulfurized heavy fraction originating from step c) and d) are suitable for direct processing for a gasoline pool. This option is preferably used if the gasoline fraction injected in step a) through the inlet of the line is a wide gasoline fraction, i.e. having a boiling point range from about the boiling point of hydrocarbons containing 2 or 3 carbon atoms (C2 or C3), up to about 250 ° C or more preferably from the boiling point of hydrocarbons containing 2 or 3 carbon atoms (C2 or C3), up to about 220 ° C or more preferably from about the boiling point of hydrocarbons containing 5 carbon atoms, up to about 220 ° C. It can also be used with light gasoline, i.e. having a final boiling point below 210 ° C.

In this embodiment, the catalyst bed preferably consists of a single catalyst bed of cobalt-molybdenum type.

The final light gasoline fraction recovered from the top of the column and the desulfurized heavy fraction recovered from the bottom of the column are gasoline fractions desulfurized to a very low sulfur content, i.e. having a sulfur content of less than 50 ppm mass and preferably less than 30 ppm. or 10 ppm mass The final light gasoline fraction is mainly a fraction whose boiling point range is usually from about the initial boiling point of the feed in the catalyst column, mainly from 80 to 120 ° C, to about 145 ° C, or preferably to about 160 ° C or more preferably up to about 180 ° C. The desulfurized heavy fraction is mainly a fraction whose boiling point range is usually from about the final boiling point of the final light gasoline fraction to about the final boiling point of the feed in the catalyst column, mainly from 220 to 250 ° C. Both fractions recovered at the outlet of the catalyst column can then be mixed and sent to the stripper to remove the last dissolved traces of H ₂ S for final transfer to the gasoline pool.

In a second embodiment, the feedstock in step c) contains an intermediate heavy gasoline fraction originating from step b) and all or part of a recirculated desulfurized heavy fraction taken from the bottom of the catalyst column. This option is used in particular when the gasoline fraction injected in step a) through the inlet of the line is a light gasoline fraction with a final boiling point below 220 ° C, for example, below or equal to 210 ° C, below or equal to 180 ° C, below or equal to 160 ° C or lower or equal to 145 ° C.

However, if the intermediate heavy gasoline fraction recovered from the bottom of the distillation column in step b) has a final boiling point of about 180 ° C., it is desirable to additionally introduce the external heavy gasoline fraction as recirculation to maintain the liquid phase in the catalyst column in selected working conditions. This recycling thus allows the catalyst to be flushed at the bottom, which is desirable if the feed at the hydrodesulfurization step contains coke precursors and resins.

Preferably, the simple additional introduction of the heavy fraction is carried out in a recycle stream and said heavy fraction is returned to the column along the loop. This external recycle gasoline fraction typically has a distillation range from the final temperature of the processed feed, i.e. in the range from 145 ° C. to about 210 ° C. in this embodiment, to a temperature of about 180 ° C. to 240 ° C. This external recycle fraction may, for example, be a desulfurized cracked heavy gasoline fraction. The external recirculation heavy fraction should have a low unsaturated content to be used as a solvent for optimal washing of the catalyst.

In this embodiment, the catalytic column preferably contains two catalytic layers located respectively above and below the place of input of raw materials into the column. Preferably, a catalyst having both the hydrodesulfurization and hydrogenation properties is loaded onto the bottom of the catalyst column. A catalyst containing at least one metal of group VIII and at least one metal of group VIb in the form of a sulfide, in which preferably the metal of group VIII is nickel and the metal of group VIb is molybdenum. The catalyst in the upper zone, in contrast, is preferably a cobalt-molybdenum catalyst.

In the third embodiment, three different fractions are withdrawn from the catalyst column:

- desulfurized final light gasoline fraction withdrawn from the top of the column and suitable for processing for a pool of gasoline,

- a desulfurized heavy fraction discharged from the bottom of the column, most of which is recycled to the catalytic distillation column;

- and additional desulfurized gasoline fraction, derived from the point located between the place of selection of the desulfurized final light gasoline fraction and the place of selection from the bottom of the column. Preferably, this fraction is withdrawn at a point located between the place of introduction of the raw materials into the column and the place of selection from the bottom of the column.

This option is preferably used if the gasoline fraction injected in step a) through the inlet of the line is a wide gasoline fraction, i.e. having a boiling range of usually from about the boiling points of hydrocarbons containing 2 or 3 carbon atoms (C2 or C3), to about 250 ° C, or preferably from about the boiling points of hydrocarbons containing 2 or 3 carbon atoms (C2 or C3), up to about 220 ° C, or more preferably from about the boiling points of hydrocarbons containing 5 carbon atoms, up to about 220 ° C. This option is also preferable if the catalytic column is to operate with very high degrees of conversion (deep desulfurization), therefore, at high temperature, in particular if the final temperature of the fraction processed by the method of the invention is particularly high and, therefore, the feed contains heavy sulfur-containing compounds such as thiophene or benzothiophene, which are difficult to desulfurize.

Recycling of the heavy fraction into the catalyst column allows, despite the high temperature, to retain the liquid phase in the column and thus allows to increase the washing speed of the catalyst located in the lower part. Indeed, operation at a higher temperature promotes the formation of coke and resins during the polymerization of the diolefins contained in the feed, in particular in the lower part of the column, where the temperatures are the highest.

Preferably, an external hydrocarbon fraction is additionally introduced into the recirculation loop. This external heavy fraction usually has a distillation range from 220 ° C to 270 ° C, preferably from 220 ° C to 250 ° C. This heavy fraction is mainly a cracked heavy fraction originating from an FCC fraction, for example, LCO (Light Cycle Oil, i.e., a fraction obtained by catalytic cracking and boiling in a temperature range that is higher than the temperature range of gasoline) or a kerosene fraction or direct-run gazole gas oil fraction.

In this embodiment, the catalytic column preferably contains two catalytic layers located respectively above and below the place of input of raw materials into the column. The catalyst located in the catalytic zone at the bottom of the column is preferably a nickel-molybdenum type catalyst. The catalyst located in the upper zone is preferably a cobalt-molybdenum type catalyst providing good selectivity for hydrodesulfurization reactions compared to olefin hydrogenation reactions to preserve the octane number of the processed feed.

The final light gasoline fraction recovered from the top of the column and the desulfurized additional gasoline fraction recovered as side distillation are gasoline fractions desulfurized to a low sulfur content, i.e. with a sulfur content of less than 50 ppm mass and preferably less than 30 ppm. or 10 ppm mass The final light gasoline fraction is mainly a fraction, the boiling point of which is usually from about the initial boiling temperature of the raw materials processed in the catalytic column (mainly from 80 to 120 ° C), to about a temperature above 145 ° C, or preferably to about above 160 ° C or more preferably up to about 180 ° C. The desulfurized additional gasoline fraction is mainly a fraction whose boiling point range is usually from about the final boiling point of the final light gasoline fraction to about the final boiling point of the second intermediate heavy gasoline fraction starting from step b), i.e. up to a temperature of between 210 and 230 ° C. Both fractions recovered at the outlet of the catalytic column (final light gasoline fraction and desulfurized additional gasoline fraction) can then be mixed and sent to the stripper to remove the last dissolved traces of H ₂ S, followed by final storage in a gasoline pool.

Brief Description of the Figures

These aspects, as well as other aspects of the invention, will be apparent from a detailed description of methods for carrying out the invention with reference to the drawings, in which:

- figure 1 shows a first diagram of a method according to the invention;

- figure 2 shows a second diagram of a method according to the invention;

- figure 3 shows a third diagram of a method according to the invention;

- figure 4 shows a fourth diagram of a method according to the invention.

In the figures, similar elements are usually denoted identically.

Figure 1 shows the first diagram of a method according to the invention for processing gasoline feedstocks, in particular containing diolefins, oleins and sulfur-containing compounds such as mercaptans and from the thiophene group, to produce several gasoline fractions with a total sulfur content of less than 50 ppm. (mass.), preferably less than 30, even less than 10 ppm mass

According to the method, the gasoline feed to be processed, possibly with additional loading of hydrogen, is sent to the demercaptization reactor 2 via loading line 1.

Reactor 2 includes a catalytic section provided with a catalytic layer specially selected for the selective attachment of mercaptans to olefins in order to increase their molecular weight.

Preferably, the reactor is a fixed catalyst bed reactor that operates in a three-phase or two-phase system and one of whose phases (catalyst) is solid.

Demercaptization reactions proceed mainly at a temperature of from 50 to 250 ° C, under a pressure of from 0.6 to 2 MPa and with a bulk velocity of liquid from 0.5 h ^-1 to 10 h ^-1 .

The stream leaving stage a) of the demercaptization is then sent to fractional column 4, also called a “splitter”, through line 3. Fractional column 4 is configured to separate an intermediate light gasoline fraction with a low sulfur content and an intermediate heavy gasoline fraction containing most of the sulfur initially present in the gasoline to be treated. The operating pressure in this column is mainly from 0.1 to 2 MPa and preferably from 0.6 to 1 MPa. The number of theoretical plates in this fractional column is generally from 10 to 100, and preferably from 20 to 60. The reflux ratio, expressed as the ratio of liquid movement in the column divided by the distillate flow rate, expressed in kg / h, is mainly less than 1 and preferably less 0.8. Intermediate light gasoline obtained by separation mainly contains at least a plurality of C5 olefins, preferably C5 compounds and at least 20% C6 olefins. Mostly this light fraction contains a very small amount of sulfur, i.e. less than 50 ppm masses, preferably less than 30 ppm mass., even less than 10 ppm mass Additional processing of the light fraction to its use as base gasoline is not necessary.

As shown in FIG. 1, the intermediate light gasoline fraction withdrawn from the top of the fractionation column through line 5 is cooled by a heat exchanger 6, then transferred to a gas-liquid separator 9. A gas stream containing non-condensable compounds, mainly hydrogen, is removed from the bottom separator along line 9, while the liquid gasoline fraction is withdrawn from the bottom along line 10, part of which serves to load a pool of gasoline (via line 11), and the other part corresponds to distillation reflux.

The intermediate heavy gasoline fraction withdrawn from the bottom of fractionation column 4 and containing most of the sulfur-containing products, including those that were formed during stage a) of demercaptization, serves as a raw material in the third stage of the method according to the invention.

In Figure 1, an intermediate heavy gasoline fraction is sent via line 13 to a catalytic distillation column 14 provided with a reaction zone 15 containing at least one catalyst bed. According to the invention, the catalyst is selected so that it is capable of decomposing sulfur-containing compounds to H ₂ S in the presence of hydrogen, providing selectivity for the hydrogenation of olefins to preserve the octane number of the feed. The hydrodesulfurization catalyst is used in its sulfide form and it contains a porous carrier of at least one metal of group VIII, at least one metal of group VIb. Preferably, the catalyst used in the process of the invention in the embodiment of Figure 1 is a cobalt-molybdenum type catalyst.

To carry out the catalytic conversion of sulfur-containing compounds, hydrogen is supplied via line 16.

The catalytic distillation column 14 is configured to fractionate said intermediate heavy gasoline fraction into at least two fractions, namely a final desulfurized heavy gasoline fraction and a final desulfurized light gasoline fraction. Both fractions: the final desulfurized heavy gasoline fraction and the final desulfurized light gasoline fraction can then be sent to the stripper to remove the last dissolved traces of H ₂ S (not shown).

As shown in FIG. 1, the intermediate heavy gasoline fraction originating from step b) is brought into contact in the reaction section 15 with hydrogen supplied via line 16 and a hydrodesulfurization catalyst for converting sulfur-containing compounds to H ₂ S. Simultaneously with the conversion reaction, intermediate fractionation heavy gasoline fraction to obtain the final light gasoline containing H ₂ S formed during the decomposition of sulfur-containing compounds. The final light gasoline is removed from the upper part of the distillation column through a pipe 17.

The final light gasoline fraction distilled in the upper part of the fractionation column, together with Н ₂ S, formed as a result of desulfurization reactions, and hydrogen, which did not enter into interaction in the column, are then cooled by means of heat exchanger 18, then they are transferred through pipeline 19 to gas-liquid separator 20 where a gas stream is separated, containing mainly hydrogen and H ₂ S (line 21) and desulfurized heavy gasoline. The desulfurized heavy gasoline is then divided into two fractions, one of which is recycled to the distillation column 14 to provide reflux and the other fraction, which can be used in the gas pool after possible passage through the H ₂ S stripper. Gases from the upper part can be transferred to the amine absorption unit for separation of hydrogen from hydrogen sulfide for hydrogen purification and possible recycling. The method according to the invention, presented in figure 1, relates mainly to the processing of a wide gasoline fraction.

The second embodiment of the method according to the invention is shown in figure 2. This embodiment mainly differs from the first embodiment by the presence of a recycle stream of the fraction from the bottom of the catalyst column to the place of introduction of the feed into the column. In Figure 2, a fraction of the stream exiting through line 25 is mixed with intermediate heavy gasoline in line 26 and is thus returned to the catalytic distillation column. An additional introduction of the external heavy fraction is carried out along line 27 into this recycle stream. Release 29 is provided in this chain. Recycling of the heavy fraction through the inlet to the catalyst column allows, despite the high temperature in the lower part of the column, to maintain the liquid phase in the column and thus increases the flow rate for washing the catalyst in the lower part. This flushing from resins and coke resulting from the presence of highly unsaturated compounds in the intermediate heavy gasoline fraction provides the catalysts used with a long cycle with a high degree of conversion. The catalytic column preferably contains two catalytic layers located respectively above and below the place of input of raw materials. The catalyst in the catalytic zone located at the bottom of the column is preferably a nickel-molybdenum type catalyst. The catalyst in the upper zone is preferably a cobalt-molybdenum catalyst.

A third embodiment of the method according to the invention is shown in Figure 3. This embodiment mainly differs from the second embodiment in that the additional desulfurized heavy gasoline fraction is discharged through line 28 at a point located between the feed inlet and the bottom of the column.

A fourth embodiment of the method is shown in FIG. 4. This embodiment has the same characteristics as the method of FIG. 1 and provides, in step b) of fractionation in the distillation column 4, an additional lateral distillation of the gasoline fraction, the boiling point of which is in the range from the final the boiling point of the intermediate light gasoline fraction; and the initial boiling point of the intermediate light gasoline fraction. In figure 4, the gasoline fraction is withdrawn in the form of lateral distillation from the distillation column 4 along line 25. The withdrawal point along line 25 is located in the column between the outlet at the upper part along line 5 and the outlet from the bottom of the column. Preferably, the withdrawal is carried out over the feed line through line 3 to column 4. This gasoline fraction is sent to a hydrodesulfurization unit 26, which is intended to be converted in the presence of hydrogen, in particular mercaptans and compounds such as thiophenes present in said fraction, into H ₂ S. Installation 26 consists of a chamber containing at least one layer of a hydrodesulfurization catalyst.

Preferably, the hydrodesulfurization catalyst includes at least one support, at least one Group VIII metal (Groups 8, 9 and 10 of the new Periodic Classification Handbook of Chemistry and Physics, 76th Edition, 1995-1996) and at least one Group VIb metal (group 6 of the new periodic classification Handbook of Chemistry and Physics, 76th edition, 1995-1996). Preferably, the density of Group VIb metals of the catalyst per unit surface area of the carrier is (including limit values) from 2.10 ^-4 to 18.10 ^-4 g of Group VIb metal oxides per m ^{2 of} carrier, preferably (including limit values) is from 3.10 ^{- 4} to 16.10 ^-4 g of Group VIb metal oxides per m ^{2 of} carrier material, more preferably (including limit values) from 3.10 ^-4 to 14.10 ^-4 g of Group VIb metal oxides per m ^{2 of} carrier material, is very preferably (including limit values) from 4.10 ^-4 to 13.10 ^-4 g of Group VIb metal oxides per m ² n the settler.

The content, expressed with respect to the total weight of the catalyst, of Group VIb metals, is preferably (including limit values) from 1 to 20% of the mass. metal oxides of group VIb, more preferably is (including limit values) from 1.5 to 18% of the mass. Group VIb metal oxides are very preferably constituted (including limiting values) from 2 to 15% by weight. metal oxides of group VIb, even more preferably is (including limit values) from 2.5 to 12% of the mass. Group VIb metal oxides. Preferably, the metal of group VIb is molybdenum or tungsten, or a mixture of the two metals, and more preferably the metal of group VIb is only molybdenum or tungsten. The metal of group VIb is very preferably molybdenum.

The content, expressed with respect to the total weight of the catalyst, of Group VIII metals of the catalyst, is preferably (including limit values) from 0.1 to 20% by weight. Group VIII metal oxides are preferably (including limiting values) from 0.2 to 10% by weight. metal oxides of group VIII and more preferably is (including limit values) from 0.3 to 5% of the mass. Group VIII metal oxides. Preferably, the metal of group VIII is cobalt or nickel, or a mixture of the two metals, and more preferably the metal of group VIII is only cobalt or nickel. Group VIII metal is very preferably cobalt.

The molar ratio of the metals of group VIII to the metals of group VIb is mainly (including limit values) from 0.1 to 0.8, preferably is (including limit values) from 0.2 to 0.6, more preferably is (including limit values) from 0.3 to 0.5.

The hydrodesulfurization catalyst may further comprise phosphorus. The phosphorus content is preferably (including limit values) from 0.1 to 10% of the mass. P ₂ About ₅ , more preferably is (including limit values) from 0.2 to 5% of the mass. P ₂ About ₅ , very preferably is (including limit values) from 0.3 to 4% of the mass. P ₂ About ₅ , even more preferably is (including limit values) from 0.35 to 3% of the mass. P ₂ About ₅ , in relation to the total weight of the catalyst.

If phosphorus is present, the molar ratio of phosphorus to group VIb metal is mainly greater than or equal to 0.25, preferably greater than or equal to 0.27, more preferably is (including limit values) 0.27 to 2, even more preferably is (including limit values) from 0.35 to 1.40, very preferably is (including limit values) from 0.35 to 1.10, even more preferably is (including limit values) from 0.45 to 1.0, even makes (including limit values) from 0.50 to 0.95.

The catalyst carrier is a porous solid selected from the group consisting of: aluminum oxides, silicon oxides, silicon oxides — aluminum oxides or titanium or magnesium oxides, used individually or in admixture with alumina or silica — alumina. It is preferably selected from the group consisting of: silicon oxide, a group of transition aluminas and silica-alumina, very preferably the support mainly consists of at least transition alumina, i.e. contains at least 51% by weight, preferably at least 60% by weight, very preferably at least 80% by weight, even at least 90% by weight. transition alumina. It can only consist of transition alumina.

The specific surface area of the support used to obtain the catalyst, before the introduction of metals of groups VIb and VIII and possibly molding and heat treatment, is mainly less than 200 m ² / g, preferably less than 170 m ² / g, more preferably less than 150 m ² / g very preferably less than 135 m ² / g, even less than 100 m ² / g and even less than 85 m ² / g. The carrier can be obtained using any precursor, by any method of preparation and using any molding device known to those skilled in the art.

Examples

In a fixed bed, downflow reactor, 1000 cc of NiMo 8/8 catalyst is loaded on a nickel aluminate support in the form of spheres 2-4 mm in size. It is sulfonated first by injection for 4 hours at VVH = 2 h ^-1 at 350 ° C and 2.5 MPa of a heptane feed containing 4% DMDS at a hydrogen flow rate of 500 N liters / liter. Under these conditions, DMDS decomposes to H ₂ S and provides sulfonation of the catalyst.

The raw material used for the pilot test is FCC gasoline, whose initial boiling point is PI = 2 ° C, and the final boiling point of which is PF = 208 ° C.

The operating conditions are as follows:

P = 1.0 MPa

T = 100 ° C

VVH = 3 h ^-1

H ₂ / HC = 2 N liters / liter.

Analysis of the chemical composition of sulfur-containing compounds gives the following results: Connections Raw materials (ppm) Outflow (ppm) RSH C1-C3 83 2 Sulfur Outside RSH C1-C3 857 938 Total 940 940

It was noted that under these conditions, the conversion of mercaptans from C1 to C3 reaches 97.6%. These mercaptans are sulfur-containing compounds that most likely end up in the light gasoline fraction after distillation.

Chromatographic analysis of the feed and the effluent gives the following results for hydrocarbon groups: Connections Raw materials Output stream Paraffins (%) 29.0 28.9 Olefins (%) 50,0 49.8 Naphthenes (%) 8.8 8.9 Aromatic compounds (%) 12,2 12,2 C5 diolefins (%) 0.31 0.26 MAV (mg / g) 12.1 11.6

It was noted that olefins were hardly hydrogenated between the inlet and outlet of the reactor. Consequently, the octane number has not decreased.

In addition, the chromatographic method used allows the identification of C5 diolefins that are derived from the group of olefins. These diolefins are: isoprene, 1,3-cispentadiene and 1,3-transpentadiene. The degree of conversion in the reactor is approximately 17%.

Finally, the MAV (Maleic Anhydride Value) measurement provides information on the amount of highly unsaturated compounds present in the effluent. It was noted that the effluent from the reactor had a MAV value very close to the feed.

The stream leaving the reactor is then separated in a distillation column in a batch mode. The flow is directed to a 100 L reboiler heated by resistances, while condensation in the upper part of the column is provided with water with glycol addition in order to prevent the loss of light compounds. The temperature of the water with the addition of glycol is 15 ° C.

The column has a diameter of 10 cm and a lining (multiknit buffers) at a height of 2 m. Separation is carried out with a reflux ratio of 15. The separation pressure is atmospheric pressure. If the thermocouple in the upper part reaches a temperature of 65 ° C, and the temperature in the lower part is about 90 ° C, distillation stops. The required separation temperature is 65 ° C.

This periodic distillation allows separation in the experimental mode, reproducing an industrial splitter having the following characteristics:

- 40 theoretical plates;

- pressure in the flask of the reflux condenser: 0.9 MPa;

- reflux ratio: 0.9;

- separation temperature: 65 ° C.

The light gasoline fraction recovered from the top of the column contains 32.8% of the mass. source gasoline.

The characteristics of the products recovered from the top of the column (after distillation of the resulting H ₂ S) and from the bottom are as follows: Top fraction Bottom fraction The degree of extraction (%) 32.8 67.2 PI (° C) 2.0 63.0 PF (° C) 64.8 208.0 Paraffins (%) 33,4 26.7 Olefins (%) 65.0 42,4 Naphthenes (%) 0.9 12.8 Aromatic compounds (%) 0.5 17.9 MAV (mg / g) 5.2 14.7 RSH C1-C3 (ppm) 6 0 Sulfur outside RSH C1-C3 (ppm) four 1394 Total sulfur (ppm) 10 1394

The combination of a demercaptization reactor with a splitter thus allows the output of an intermediate light gasoline fraction having a low sulfur content.

The heavy gasoline fraction originating from the bottom of the splitter is then sent to a catalytic distillation column. This heavy gasoline fraction, called intermediate, has a slightly higher MAV as a result of separation than the feedstock.

The intermediate heavy gasoline fraction is injected into the catalytic distillation column with a diameter of 5 cm and a height of 12 m

Into this column, 0.75 kg of cobalt and molybdenum hydrodesulfurization catalyst are loaded on a sulphide-supported alumina carrier. This catalyst contains 3% of the mass. cobalt in the form of oxide and 10% of the mass. molybdenum in the form of oxide. Raw materials are injected in the presence of hydrogen so that 70% of the mass. the catalyst is at the level of the input of raw materials. The catalytic distillation column operates under the following operating conditions:

- pressure in the upper part of the column: 1.6 MPa

- temperature in the upper part of the layer: 270 ° C

- temperature in the lower part of the layer: 315 ° С

- the ratio of hydrogen to the consumption of raw materials: 100 Nm ³ / m ³

- reflux ratio: 2

The results related to the fraction in the upper part
(after degassing of H ₂ S) and fractions in the lower part are as follows: Top fraction Bottom fraction The degree of extraction (%) 86.4 13.6 PI (° C) 61.2 142.3 PF (° C) 147.0 208.2 Paraffins (%) 43.3 34.7 Olefins (%) 28.7 16.1 Naphthenes (%) 11.7 19.9

Aromatic compounds (%) 16.3 29.3 Total sulfur (ppm S) 34 3 HDO (%) 36.1 38.9 HDS (%) 97.2 98.4

Claims (22)

1. A method of treating gasoline containing diolefins, oleins and sulfur compounds, including mercaptans, said method comprising the following steps: a) carry out the stage of demercaptization by adding at least part of the mercaptans to olefins by bringing gasoline into contact with at least the first catalyst at a temperature of from 50 to 250 ° C, a pressure of from 0.4 to 5 MPa and with a liquid volume velocity (LHSV) from 0.5 to 10 h ^-1 , wherein the first catalyst is sulfide and contains a first carrier of at least one metal selected from group VIII and at least one metal selected from group VIb of the Periodic table of elements, the first the catalyst has the following characteristics ISTIC: a carrier consisting of a gamma modification of alumina with a specific surface area of 180 to 270 m ² / g, the metal content of group VIb, expressed in the form of oxide, is from 4 to 20 wt.% with respect to the total weight of the catalyst, the content of the metal of group VIII, expressed in the form of oxide, is from 3 to 15 wt.% in relation to the total weight of the catalyst, the molar ratio of the metal of group VIII and the metal of group VIb is from 0.6 to 3 mol / mol; b) fractionation of gasoline leaving stage a) is carried out in a distillation column to at least a first intermediate light gasoline fraction with a total sulfur content that is lower than that of the original gasoline, and a second intermediate heavy gasoline fraction containing most of the initial sulfur-containing compounds; c) introducing a stream of hydrogen and at least a second intermediate heavy gasoline fraction exiting from step b) into a catalytic distillation column (14) including at least one reaction zone (15) containing at least one second catalyst in a sulfide form containing a second support, at least one metal of group VIII and one metal of group VIb, with a metal content of group VIII, expressed in the form of oxide, comprising from 0.5 to 25 wt.% with respect to the weight of the catalyst, and the metal content groups VIb, expressed in f in the form of oxide, comprising from 1.5 to 60 wt.% with respect to the weight of the catalyst, the conditions in the catalytic distillation column being chosen so that in the presence of hydrogen contact intermediate heavy gasoline leaving step b) is contacted with the second catalyst for cleavage sulfur-containing compounds up to H ₂ S, while contacting with the second catalyst is carried out at a pressure of from 0.1 to 4 MPa and at a temperature of from 210 to 350 ° C; d) at least one final light gasoline fraction containing H ₂ S and a desulfurized heavy gasoline fraction are withdrawn from the catalytic distillation column, the final light gasoline fraction is withdrawn at a point located above the reaction zone, and the sulfur-rich heavy gasoline fraction is withdrawn at a point located under the reaction zone. 2. The method according to p. 1, in which bringing into contact with the second catalyst in stage c) is carried out under pressure from 1 to 3 MPa and at a temperature of from 220 to 320 ° C. 3. The method according to p. 1 or 2, in which the first catalyst contains nickel or molybdenum and in which the mass percentage of nickel, expressed by oxide, in relation to the total mass of the catalyst is from 4 to 12% and the mass percentage of molybdenum, expressed by oxide, ranges from 6 to 18% with respect to the total weight of the catalyst. 4. The method according to p. 1 or 2, in which the second catalyst contains cobalt or a metal of group VIb selected from molybdenum and tungsten. 5. The method according to p. 1 or 2, in which the second catalyst contains a mass% of a metal of group VIII, expressed by oxide, comprising from 1 to 10% with respect to the total weight of the catalyst. 6. The method according to p. 1 or 2, in which the second catalyst contains a mass% of a metal of group VIb, expressed by oxide, comprising from 3 to 50% with respect to the total weight of the catalyst. 7. The method according to p. 1 or 2, in which the second catalyst contains cobalt and molybdenum. 8. The method according to claim 1 or 2, in which the desulfurized heavy gasoline fraction leaving step c) is partially returned to the catalytic distillation column (14). 9. A method according to claim 1 or 2, in which an additional hydrocarbon fraction, which serves as a recycle stream, is introduced into the catalytic distillation column (14) to maintain the liquid phase in the lower part of the specified column. 10. The method according to p. 1 or 2, in which stage a) is carried out under a pressure of from 0.6 to 1 MPa and with a flow rate of H ₂ / feed rate of 0.5 to 2 Nm ^{3 of} hydrogen per m ^{3 of} feed. 11. The method according to claim 1 or 2, in which the distillation column includes a first and second catalytic layers, respectively containing a cobalt-molybdenum catalyst and a nickel-molybdenum catalyst, the first catalyst being located above the second catalyst. 12. The method according to p. 1 or 2, in which at stage b) additional lateral extraction is carried out along line (25), the extraction point of which is located in the column between the place of extraction from the upper part and the place of extraction from the lower part of the distillation column, gasoline fraction, the boiling temperature range of which is in the range from the final boiling point of the first intermediate light gasoline fraction to the initial boiling point of the intermediate heavy gasoline fraction. 13. The method according to p. 12, in which the gasoline fraction recovered in the form of side distillation is treated in a catalytic hydrodesulfurization unit in the presence of hydrogen. 14. The method according to claim 1 or 2, in which the processed gasoline comes from a catalytic cracking unit.

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