RU2638167C2 - Method of producing light gasoline with low sulfur content - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method includes the following steps: a) conducting a demercaptization step by attaching, at least, a portion of the mercaptans to the 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. The first catalyst is presented in a sulfided form and comprises 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 Elements, a weight percent expressed as the equivalent of metal oxide selected from group VIII, with respect to the total weight of the catalyst, is from 1 to 30%, and the weight percent expressed in the equivalent of metal oxide selected from group VIb is from 1 to 30% based on the total weight of the catalyst; b) carrying out the step of treating the gasoline from step a) with hydrogen in a distillation column comprising, at least, one reaction zone containing, at least, one second catalyst comprising the second carrier and, at least, one metal from group VIII. The conditions in step b) are selected such that the following operations are carried out simultaneously in the said distillation column: I) distillation with the separation of gasoline from step a) into a light gasoline fraction with a reduced content of sulfur-containing compounds and a heavy gasoline fraction having a higher boiling point, than light gasoline, and containing most of the sulfur-containing compounds, the light gasoline fraction being withdrawn at a point above the reaction zone, and the heavy gasoline fraction is withdrawn at a point located under the reaction zone; II) contacting the gasoline fraction from step a) with the second catalyst to carry out the following reactions: (i) thioetherification by attaching a portion of the mercaptans to a portion of the diolefins to produce thioethers, (ii) selective hydrogenating a portion of the diolefins to olefins and, optionally, (iii) isomerization of olefins.

EFFECT: method helps to produce a light gasoline fraction.

14 cl, 2 dwg

Description

The invention relates to a method for treating gasoline containing diolefins, olefins and sulfur-containing compounds, including mercaptans, to obtain a light fraction of this gasoline with a very low sulfur content 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. Nearly 90% of the sulfur present in reformulated gasolines comes from catalytic cracked gasoline fractions (FCC, Fluid Catalytique Cracking, or fluidized bed 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 hydroprocessing (or hydrodesulfurization) of catalytic cracking gasolines. If this additional treatment is carried out under ordinary conditions familiar to the skilled person, an even greater reduction in the sulfur content of gasoline can be achieved. However, the main disadvantage of this method is a significant decrease in the octane number of the fraction due to the saturation of olefins in the hydrotreatment process.

US Pat. No. 4,131,537 teaches interest, which is the separation of 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 metal of the group VIb 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 separation 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.

US Pat. No. 6,440,299 describes a method for removing mercaptans from hydrocarbon feeds using a catalytic distillation column. The catalytic layer of the column is located above the input level of the feedstock for processing only a light fraction of the feedstock. The catalyst used is a catalyst with a nickel sulfide carrier on which mercaptans are removed by a thioesterification reaction by addition to diolefins. As shown in the example given in this patent, the simultaneous production of a very low sulfur content in the light fraction of the processed raw materials in this way is difficult to achieve. Indeed, if the amount of diolefins in the feed is small and / or if the amount of mercaptans is significant, the kinetics of the conversion of mercaptans on the catalyst does not contribute to such a conversion. To maintain a high degree of conversion, either increase the temperature or limit internal movements in the column. An increase in temperature until a constant temperature of distillation of a light gasoline fraction can be achieved can only occur with an increase in pressure in the column, while this increase is limited by the design of the column. The disadvantage of limiting internal movements (by lowering, for example, the value of the internal reflux ratio) is the deterioration of the separation ability of the column, which would facilitate the collection of concentrations of unconverted light mercaptans in the light fraction.

Also known is US Pat. No. 5,807,477, which discloses a method for treating catalytic cracking gasoline using a first thioesterification step in which mercaptans are reacted with diolefins of a feed in the presence of a Group VIII metal oxide catalyst. The gasoline from this first stage is then sent to a distillation column including a catalytic hydrogenation section containing another Group VIII metal oxide catalyst. The catalytic column is configured to function as a depentanizer. Thus, compounds containing a carbon number greater than or equal to 6 and including thioesters formed in the first stage are extracted from the bottom of the column, while compounds containing a number of carbon atoms less than or equal to 5 are collected after distillation in the upper part of the column and they are brought into contact with a hydrogenation catalyst, where selective hydrogenation of diolefins that do not enter into the reaction at the first stage takes place.

However, by the method described above, it is difficult to obtain a light gasoline fraction that meets future sulfur specifications, i.e. with an upper limit to the total sulfur content of gasoline of 50 ppm mass., even 30 or 10 ppm mass in some countries.

As indicated in the example of US Pat. No. 5,807,477, in the first step of the process, light mercaptans do not undergo conversion or are subjected to a small degree. Indeed, the removal of mercaptans occurs by addition to the diolefins contained in the feed. The patent states that such a catalyst based on a Group VIII metal oxide also catalyzes the selective hydrogenation of diolefins. Both reactions involving diolefins thus occur simultaneously, which limits conversion along the thioesterification pathway. After introduction into the column (second stage), light mercaptans, in particular those that are more boiling compared to the separation temperature of the column, will be in the vapor phase in the distillation zone and their conversion on the catalytic layer will be difficult. The light gasoline fraction obtained in the upper part of the catalyst column thus contains a significant portion of the light mercaptans present in the feed.

Also, in the example given in the patent, it was noted that at this stage the conversion of H ₂ S does not occur at all, which means that if H ₂ S is present in the feedstock, it will inevitably end up in a catalytic column located downstream. It is known to those skilled in the art that Group VIII metal oxide hydrogenation catalysts also catalyze the addition of H ₂ S to diolefins and / or olefins, which can cause the formation of additional mercaptans at the top of the column, which will also mainly be present in the light gasoline fraction. H ₂ S and mercaptans are best known as inhibitors of this type of catalyst, in particular if the Group VIII metal is palladium.

Thus, using the invention, such as presented in US 5807477, it is difficult to achieve low sulfur content in the light gasoline fraction, which will require further processing of this fraction in order to meet the technical requirements.

The aim of the invention, therefore, is a method for producing light gasoline with a very 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., while limiting the reduction of the octane number, which is relatively simple and requires the lowest possible investment.

SUMMARY 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 carrying out the reaction of 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, a pressure of from 0.4 to 5 MPa and a liquid volume velocity (LHSV ) from 0.5 to 10 h ^-1 , wherein the first catalyst is 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 the equivalent of a metal oxide selected from group VIII, with respect to the total weight of the catalyst, is from 1 to 30% and the mass percentage expressed in the equivalent of metal oxide selected from group VIb is from 1 to 30% with respect to the total weight of the catalyst ;

b) carry out the processing stage of the gasoline obtained in stage a), hydrogen in a distillation column comprising at least one reaction zone containing at least one second catalyst containing a second carrier and at least one metal from group VIII, when this condition in stage b) is chosen so that in the specified distillation column simultaneously carry out the following operations:

I) distillation with the separation of gasoline obtained in stage a) into a light gasoline fraction with a low content of sulfur-containing compounds and a heavy gasoline fraction, the boiling point of which is higher than the boiling point of light gasoline, containing most of the sulfur-containing compounds, and such a light gasoline fraction is taken at a point located above the reaction zone, and the heavy gasoline fraction is taken at a point located under the reaction zone;

II) bringing into contact the gasoline fraction obtained in stage a) with a second catalyst for the following reactions:

(i) thioesterification by carrying out the reaction of attaching part of the mercaptans to part of the diolefins to obtain thioethers,

(ii) selectively hydrogenating a portion of the diolefins to form olefins and optionally

(iii) isomerization of olefins.

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 interaction of mercaptans with 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 with olefins, which are mainly present in very large quantities. The lightest mercaptans are the most reactive in this first step 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 selected conditions. The removal of H ₂ S already at this first stage is an advantage to the extent that it allows to prevent the inhibition of the catalyst of the catalytic column in the second stage (since H ₂ S is an inhibitor of the used catalyst) and to avoid getting H ₂ S at the top of the column together with a light fraction . The conversion of H ₂ S before entering the distillation column into heavy mercaptans or sulfides, which enrich the heavy fraction in the catalytic distillation column, provides a very low sulfur content in the light fraction. Thus, it was possible to achieve 100% conversion of H ₂ S present in the feed in an amount of about 10 ppm. mass

Demercaptization and H ₂ S removal reactions are 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 the group VIb (group 6 of the new periodic classification Handbook of Chemistry and Physics, 76th edition, 1995-1996) and the carrier.

The Group VIII metal is preferably selected from nickel and cobalt, and in particular nickel. The Group VIb metal is preferably selected from molybdenum and tungsten, and preferably molybdenum.

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) treating the gasoline obtained in step a) in a distillation column having a reaction zone.

The configuration of the distillation column ensures operation under operating conditions that allow at the same time:

- to carry out the conversion of light mercaptans, which did not interact in stage a), by thioesterification with diolefins so that the thioesters formed in the second stage mainly fall into the heavy gasoline fraction. The catalyst used in the distillation column also promotes the selective hydrogenation of diolefins and possibly allows olefins to be isomerized by displacement of the double bond from an external position to an internal position.

- separate the gasoline pretreated in step a) into at least two fractions, namely a gasoline fraction called “light” depleted in sulfur-containing compounds and containing most of the olefins, and a gasoline fraction called “heavy” containing most of the sulfur-containing compounds, in particular thioesters formed in stage a) and b).

The selective hydrogenation of diolefins to olefins is especially important when the light gasoline fraction is used as a feedstock for a thioesterification unit (such as TAME, for example), because these highly unsaturated compounds readily form resins during the implementation of this type of process. If this light fraction is sent directly to a pool of gasoline, hydrogenation of diolefins is also preferred, since they tend to form resins if oxygen remains in the tanks. In addition, this second step also makes it possible to weight the residual mercaptans that were not converted in step a) by reacting the residual mercaptans with diolefins. Finally, in connection with the use of a Group VIII metal selected for one of the supported catalysts in a column, preferably palladium, the invention proposes isomerization of olefins by displacement from an external position to an internal position. This isomerization is advantageous, because it allows you to save the octane number of the fraction, even improve it, despite the hydrogenation of olefins, which can occur at each stage.

An advantage of the method according to the invention is that in step a) hydrogen sulfide (H ₂ S) is not formed, but, on the contrary, it is possible to subject H ₂ S conversion, possibly present in the processed feed. Indeed, the presence of H ₂ S at the entrance to the catalytic column can, as indicated above, cause the formation of additional mercaptans in the catalytic zone of the column, which can then enter the light fraction. The absence of H ₂ S, an inhibitor of the catalyst used in the present invention, also allows to increase the efficiency of the catalyst in the catalyst column.

Another advantage of the method is that the high degree of conversion of the mercaptans in step a) significantly increases the molar ratio between the mercaptans and diolefins at the inlet to the column. The efficiency of thioeterification of residual mercaptans at stage b) therefore increases, since the mercaptans / diolefins ratio is favorable.

Another advantage of the sequence of steps a) and b) is related to the synergy of these two stages for the conversion of mercaptans having different reactivity depending on the chain length in both stages. Indeed, the lightest mercaptans (in particular, methanethiol, ethanethiol) have the highest reactivity in stage a). On the contrary, the heaviest mercaptans that can move to the light fraction (1- and 2-propanethiol), i.e. those whose boiling point is close to the separation point in the column are the least reactive in stage a), while they are most easily converted in a catalytic column, because they are present in the liquid phase at the level of the catalytic zone. The synergy of the two reactions allows, therefore, to obtain a light fraction of gasoline with a very low sulfur content, regardless of the nature of the mercaptans originally present in the feed.

Another advantage of the method according to the invention is that the desulfurization of the light gasoline fraction coming from the distillation column is not necessary, because most of the sulfur-containing compounds were converted to higher molecular weight compounds in steps a) and b) so that they were in the heavy gasoline fraction.

At the stage a), catalytic hydrogenation reactions are not carried out, hydrogen, if added, serves mainly to maintain the hydrogenating ability of the catalyst surface, providing a high yield of demercaptization reactions. Thus, low pressure does not adversely affect the method of the invention. Another advantage of the method according to the invention is, therefore, that both stages can be carried out at the same pressure (except for the loss of raw materials), because stage a) requires a small amount of dissolved hydrogen, it does not even require at all, and stage b) is usually carried out at a relatively low pressure (less than 1.5 MPa) to minimize the consumption of media, providing the temperature necessary for the thioesterification reaction. This step b) also requires a relatively small amount of additionally introduced hydrogen to selectively hydrogenate only diolefins.

DETAILED DESCRIPTION OF THE INVENTION

The object of the present invention is a method for producing a light fraction of gasoline with a low sulfur content from gasoline, preferably originating from a catalytic cracking unit, coking unit or a unit for reducing viscosity.

According to the invention, gasoline first goes to step a) of converting sulfur-containing compounds, mainly mercaptans, the lightest gasoline compounds, with olefins to increase their molecular weight. The method also includes a second stage b), which consists in supplying all or part of the gasoline coming from stage a) to a distillation column containing a catalytic reaction zone. In step b), where the gasoline is separated into at least two fractions (light fraction and heavy fraction), the light fraction is treated under conditions and using a catalyst that allows (i) to produce thioesters by adding part of the mercaptans that have not reacted on stage a), to a part of diolefins to obtain sulfur-containing compounds with a higher boiling point, which then turn into a heavy fraction, (ii) selectively hydrogenate at least a part of diolefins to olefins and possibly (iii) isomerization olefins by displacement of the double bond from the external to the internal position.

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

The method according to the invention thus makes it possible to obtain a light gasoline fraction with a total sulfur content of less than 50 ppm. mass., preferably less than 30 ppm, even less than 10 ppm mass

As used herein, the term “catalytic column” means a device in which a catalytic reaction and separation of products occur at least simultaneously. The equipment used may include a distillation column provided with a catalytic section, in which the catalytic reaction and distillation occur simultaneously with a specially selected separation point. 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 / steam circulating in direct flow or in counterflow.

The advantage of using a catalytic distillation column compared to a system containing a reactor and a distillation column is to reduce the number of individual elements, thereby reducing investment. The use of a catalytic column allows you to control the reaction, promoting the exchange of heat generated; the heat generated during the reaction can be used 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 about 250 ° C, preferably from about the boiling point of hydrocarbons containing 2 or 3 carbon atoms (C2 or C3,) to about 220 ° C, more preferably from about the boiling point of hydrocarbons, soda rzhaschih 5 carbon atoms to about 220 ° C. The method according to the invention can also handle raw materials whose final boiling points are lower than those indicated above, for example, fractions C5 - 180 ° 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 entire 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

In addition, 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 outlet from distillation stage b) into heavier sulfur-containing compounds which are transferred to the heavy gasoline fraction in distillation stage b).

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 has:

- 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 metal of group VIII and the metal of group VIb is from 0.6 to 3 mol / mol,

- 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.

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

- the mass content of the metal oxide of group VIb is from 4 to 20% of the mass. in relation to the total weight of the catalyst, preferably from 6 to 18% of the mass.,

- the mass content of the metal oxide of group VIII 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 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,

- the carrier consists of a gamma modification of alumina with a specific surface area of 180 m ² / g to 270 m ² / g.

In a preferred embodiment of the invention, a catalyst is used with a mass content of nickel oxide (in the form of NiO) of 4 to 12% by weight, with a mass content of molybdenum oxide (in the form of MoO ₃ ) of 6 to 18% by weight and mass the ratio of Nickel / molybdenum, comprising from 1 to 2.5, while the metals are deposited on a carrier consisting of only 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, 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, the formation of 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 oxide form. 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 (DMDS), 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.

In step a), the mercaptans are added to the olefins, the raw materials to be treated are brought into contact with the catalyst in sulfide form. 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: hydrogen (if present) in the reactor leads to the formation of H ₂ S by contact with mercaptan, which is attached 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.

Also, in the case of the presence of H ₂ S in the feed, it is converted to mercaptan (which can also be converted) by addition to olefins using a catalyst under the chosen conditions. This H ₂ S may be derived from recirculation gases or from additionally introduced hydrogen, which contains a certain amount of impurities. This H ₂ S may also in some cases dissolve in liquid feed.

This step can be carried out without adding hydrogen to the reactor, but preferably hydrogen is introduced together 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 / HC ratio of from 0 to 25 Nm ^{3 of} hydrogen per m ^{3 of} raw materials, preferably from 0 to 10 Nm ^{3 of} hydrogen per m ^{3 of} raw materials, very preferably from 0 to 5 Nm ^{3 of} hydrogen per m ³ raw materials and even 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 to 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 hour). The pressure is from 0.4 MPa to 5 MPa, 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) processing gasoline originating from stage a)

In a second step of the process of the invention, a distillation column is used including a catalytic reaction section. In the specified column, gasoline distilled from step a) is distilled into at least two fractions, namely:

- a fraction called "light", which contains gasoline with a low sulfur content, the boiling point of which is usually from about the initial temperature of the raw material at the entrance to the catalyst column to a final temperature, mainly from 60 ° C to 100 ° C and

- a fraction called "heavy", the boiling point of which is usually from about the final temperature of the light gasoline fraction to about the final temperature of the feed in the catalyst column and which contains most of the heavy sulfur-containing compounds, i.e. sulfur-containing compounds whose boiling point is higher than the separation temperature selected for the functioning of the column.

The distillation catalytic column includes a reaction section containing a catalytic layer designed to conduct at least a thioetherification reaction of mercaptans that did not react with olefins in step a), selectively hydrogenating the diolefins contained in the feed, and possibly olefin isomerization. To this end, the reaction section is made in a distillation column so that the "light" gasoline, which is distilled to the top of the column, is brought into contact with the catalytic layer.

The thioesterification reaction in stage b) involves the interaction of residual mercaptans with diolefins contained in gasoline originating from stage a) to form thioesters whose boiling point is higher than residual mercaptans, so that they move to the “heavy” fraction in the lower part of the catalytic the columns.

The operation of the catalyst column involves the simultaneous presence of two phases in the reaction zone, namely the liquid phase and the vapor phase, which contains most of the hydrogen and light hydrocarbons.

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

The heat, possibly released during the reaction in the catalytic column, is removed by evaporating the mixture on a distillation plate. Therefore, the temperature profile of the column is very stable and the catalytic reactions that occur on the layer located in the upper part of the column do not interfere with its operation. Also, this stability of the temperature profile provides stable kinetics of the reactions, since they are isothermal at each level of separation.

Preferably, the catalyst used in the reaction section is also capable of selectively hydrogenating diolefins contained in the “light” fraction to the corresponding olefins by introducing hydrogen. Perhaps the catalyst in the reaction section also allows isomerization of olefins with the external position of the double bond into an isomer with the internal position of the double bond.

According to the invention, the catalyst used in the reaction section contains at least one Group VIII metal supported on a porous support and may initially be in the form of extrudates of small diameter or spheres. The catalyst has a structure adapted to 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 bed.

According to a preferred embodiment, the metal can be selected from nickel and palladium. If the metal is palladium, preferably it is the only active metal in the catalyst. If the metal is nickel, the mass content of the metal of group VIII relative to the total weight of the catalyst, expressed by oxide, is mainly from 10 to 60%.

If the metal is palladium, the mass content of the metal of group VIII with respect to the total mass of the catalyst (% Pd metal) is mainly from 0.1 to 2%.

The porous catalyst support in step b) may be selected from alumina, nickel aluminate, silica, silicon carbide, or a mixture of these oxides. Preferably, alumina is used and even more preferably pure alumina.

The catalyst, especially suitable for the implementation of the attachment of residual mercaptans to diolefins and selective hydrogenation of diolefins, contains from 40 to 60% of the mass. nickel deposited on an alumina substrate.

Hydrogen is involved in the catalytic reaction, which is mixed with the light gasoline fraction that collects at the top of the column, and the mixture is contacted with a catalyst, such as described. In the reaction section, the hydrogen / diolefins molar ratio is mainly 1 to 10 mol / mol. However, it is preferable to carry out the reaction in the presence of a small excess of hydrogen with respect to the diolefins so as to avoid excessive hydrogenation of the olefins and to provide a good octane number.

The operating pressure in the catalytic distillation column is mainly from 0.4 to 5 MPa, preferably from 0.6 to 2 MPa and preferably from 0.6 to 1 MPa. The temperature in the reaction zone is generally from 50 to 150 ° C, preferably from 80 to 130 ° C.

It should be noted that this pressure can be essentially the same (with the exception of the loss of raw materials) as in the reactor in stage a). The amount of hydrogen required for stage b) is relatively small, because it mainly serves to maintain the hydrogenation state of the catalyst and to hydrogenate only diolefins to olefins. Adjusting the pressure in the column can cause a combination of two stages. So the hydrogen recovered from the flask at the top of the column can be reused. Recycled hydrogen can, for example, be injected directly into the catalytic distillation column 5 in step b) or injected together with hydrogen further introduced into the distillation column or reactor 2, and can also be injected directly into the reactor in step a).

In accordance with a particular embodiment of the invention, the pressure used in the distillation column in step b) is equal to the pressure used in the reactor in step a) except for the loss of feedstock in the hydraulic circuit.

According to another particular embodiment of the invention, light gasoline is subjected to a condensation and separation step to recover unused hydrogen.

In accordance with another particular embodiment of the invention, unused hydrogen is returned to step a) or b).

According to another particular embodiment of the invention, in step a), H ₂ S present in the gasoline to be treated is simultaneously added to the olefins.

In accordance with a particular embodiment, the distillation column is configured to operate as a depentanizer.

According to another particular embodiment, the distillation column is arranged to function as a dehexanizer.

In the framework of the invention, it is also possible to use more than one catalytic layer in the reaction zone, for example two separate catalytic layers separated by space.

Brief Description of the Drawings

These aspects, as well as other aspects of the invention, will be apparent from a detailed description of particular embodiments of the invention with reference to the drawings, in which:

- in FIG. 1 shows a first diagram of a method according to the invention;

- in FIG. 2 shows a second diagram of a method according to the invention. The figures are not drawn to scale. In the figures, similar elements are usually denoted identically.

In FIG. 1 shows a first diagram of a method according to the invention for processing gasoline feedstocks containing, in particular, olefins, diolefins and sulfur-containing compounds such as mercaptans and from the group of thiophenes to obtain a light gasoline fraction with a total sulfur content of less than 30 ppm (mass.), preferably less than 20 ppm (mass), 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.

The demercapization catalyst of the invention comprises a 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 mass percentage, expressed in equivalent metal oxide, selected from group VIII, mainly ranges from 1 to 30% relative to the total weight of the catalyst. The mass percentage, expressed as the equivalent of a metal oxide selected from group VIb, is generally from 1 to 30% based on the total weight of the catalyst.

Preferably, the Group VIII metal is selected from nickel and cobalt, and the Group VIb metal is selected from molybdenum and tungsten.

Demercaptization reactions proceed mainly at a temperature of from 50 to 250 ° C, under a pressure of 0.4 to 5 MPa and a VVH of 0.5 h ^-1 to 10 h ^-1 .

All or part of the feedstock processed in the mercaptan weighting reactor 2 is then sent via pipeline 3 to a distillation column 4 containing a reaction zone 5 provided with a catalytic layer, the system also referred to as the “catalytic column”. Despite the fact that in FIG. 1 shows a reaction zone 5 containing only one catalytic bed, more than one catalytic bed can be used, the layers being arranged in a column in series.

The catalytic column is configured to fractionate the gasoline feed processed in reactor 2 into two fractions, namely, a heavy fraction and a light fraction. In addition, the catalytic layer is located in the upper part of the specified column so that the light fraction is in contact with the catalytic layer during fractionation. In the framework of the invention, the top of the column, which includes reaction zone 5, is used to carry out not only the weighting reaction of light mercaptans that did not react in reactor 2, but also the selective hydrogenation of diolefins present in the light fraction, even the isomerization of olefins. To this end, the light fraction is brought into contact in the presence of hydrogen with at least one catalyst located in the reaction zone 5, which contains a support and at least one metal of group VIII of the periodic table of elements.

As shown in FIG. 1, hydrogen is sent directly to the catalytic column 5 through a conduit 6, the inlet of which is located behind the reaction zone. However, it should be noted that hydrogen can be mixed directly with the stream leaving the reactor 2 at the level of line 3 before the stream moves into the catalytic column, as shown by the dashed line in FIG. one.

As shown in FIG. 1, a light fraction containing low sulfur gasoline, unreacted hydrogen, and possibly some hydrogen sulphide, is withdrawn through line 8. The fraction is then partially condensed to separate non-condensable compounds by passing through a heat exchanger 9 before being sent to a separator 11 The latter allows you to extract through line 14 a gaseous fraction containing mainly hydrogen and processed gasoline, part of which is sent via line 13 to the pool of gasoline, and the other part is returned via line 12 to the catalyst cally column 4 for the last irrigation. Hydrogen recovered from the gaseous fraction can be recycled using a compressor. This recycling can be combined with an additional hydrogen stream entering the column or with a hydrogen stream additionally entering the reactor.

Preferably, the light fraction is recovered at the level of several trays below the top of the catalytic distillation column 5.

FIG. 2 illustrates a second embodiment, which differs from that shown in FIG. 1 by the additional presence of an intermediate side extraction 15, which, for example, allows the specific extraction of a gasoline fraction containing most of the thiophene compounds, which may be the feedstock in a secondary treatment unit such as hydrodesulfurization. This selection can be carried out under the catalytic zone, as shown in FIG. 2, or at an intermediate point in the middle of the catalytic layer.

It should also be noted that the heavy fraction, which is recovered from the lower part of the catalyst column via line 7, can be processed in a hydrodesulfurization unit to convert sulfur-containing compounds to H ₂ S, and then combined with a light gasoline fraction from the upper part of the catalyst column.

Examples

In a fixed bed, downflow reactor, 50 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 introducing for 4 hours at VVH = 2 h ^-1 at 350 ° C and 2.5 MPa heptane feed containing 4% DMDS at a hydrogen flow rate of 500 Nl / L. 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 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 Nl / L.

Analysis of the chemical composition of sulfur-containing compounds gives the following results:

The distribution of mercaptans by the number of carbon atoms is as follows:

It was noted that under these conditions, the conversion of mercaptans C1-C3 reaches 97.6%. These mercaptans are sulfur-containing compounds that are most likely to be in the light gasoline fraction after distillation, which would lead to the content of mercaptans in the light fraction exceeding 25 ppm.

Chromatographic analysis of the feed and the effluent gives the following results for hydrocarbon groups:

It was noted that the olefins were almost not hydrogenated between the inlet and outlet of reactor 2. Therefore, the octane number did not decrease.

In addition, the chromatography method used allows the identification of C5 diolefins that leave the olefin group and suggest the hydrogenation of these highly unsaturated compounds that are most likely to be in the upper fraction. These diolefins are: isoprene, 1,3-cispentadiene and 1,3-transpentadiene. The degree of conversion in the reactor is approximately 17%.

Then the flow from the reactor is directed to a catalytic column with a diameter of 5 cm and a height of 12 m. 3 m of catalyst containing 0.3% by weight are loaded into the upper part of this column. Pd on an alumina-based support.

The operating conditions are as follows:

- pressure in the upper part of the column: 0.9 MPa,

- average temperature of the catalytic layer: 130 ° C,

- exit from the upper part: 25% of the mass.,

- consumption of N ₂ / consumption of raw materials: 2 Nl / l.

The following results were obtained relating to the light fraction recovered from the upper part of the catalytic column:

- total RSH content: 1 ppm mass.,

- total content S: 8 ppm mass.,

- diolefin content: 100 ppm mass

This second step allows the conversion of mercaptans to be completed by addition to diolefins and recovery of at least 10 ppm. sulfur from the light fraction withdrawn as a side stream over the catalytic zone.

Claims (21)

1. A method of treating gasoline containing diolefins, olefins and sulfur compounds, including mercaptans, said 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, a pressure of from 0.4 to 5 MPa and a liquid volume velocity (LHSV) of 0.5 to 10 h ^-1 , wherein the first catalyst is in sulfidized form 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 percent expressed in equivalent those of a metal oxide selected from group VIII with respect to the total weight of the catalyst is from 1 to 30% and a weight percent expressed in equivalent metal oxide selected from group VIb is from 1 to 30% with respect to the total weight of the catalyst; b) carry out the processing step of gasoline from step a) with hydrogen in a distillation column comprising at least one reaction zone containing at least one second catalyst containing a second support and at least one metal from group VIII, with conditions stage b) is chosen so that in the specified distillation column simultaneously carry out the following operations: I) distillation with the separation of gasoline from step a) into a light gasoline fraction with a low content of sulfur-containing compounds and a heavy gasoline fraction, the boiling point of which is higher than light gasoline, and containing most of the sulfur-containing compounds, and the light gasoline fraction is removed at a point located above the reaction zone, and the heavy gasoline fraction is removed at a point located under the reaction zone; II) bringing into contact the gasoline fraction originating from stage a) with a second catalyst for carrying out the following reactions: (i) thioesterification by attaching part of the mercaptans to part of the diolefins to obtain thioethers, (ii) selectively hydrogenating a portion of the diolefins to olefins and optionally (iii) isomerization of olefins. 2. The method according to p. 1, in which stage b) is carried out under a pressure of from 0.4 to 5 MPa, preferably from 0.6 to 2 MPa and at a temperature of from 50 to 150 ° C, preferably from 80 to 130 ° C reaction zone. 3. The method according to any one of paragraphs. 1 or 2, in which the first catalyst contains nickel and molybdenum, wherein the mass percentage of nickel, in terms of the mass of oxide, is from 1 to 30%, preferably from 4 to 12%, relative to the total weight of the catalyst and the mass percentage of molybdenum, expressed in the oxide, is from 1 to 30%, preferably from 6 to 18%, relative to the total weight of the catalyst. 4. The method according to any one of paragraphs. 1 or 2, in which the second catalyst contains Nickel with a mass percentage of Nickel, in terms of the mass of oxide, comprising from 10 to 60% with respect to the total weight of the catalyst. 5. The method according to any one of paragraphs. 1 or 2, in which the second catalyst contains palladium with a mass percentage of palladium metal constituting from 0.1 to 2% with respect to the total weight of the catalyst. 6. The method according to any one of paragraphs. 1 or 2, in which the ratio of H ₂ / HC in stage a) is from 0 to 25 Nm ^{3 of} hydrogen per m ^{3 of} raw materials and preferably from 0.5 to 2 Nm ^{3 of} hydrogen per m ^{3 of} raw materials. 7. The method according to any one of paragraphs. 1 or 2, in which the gasoline is catalytic cracking gasoline or any cracked gasoline containing olefins, diolefins and mercaptans, pure or mixed with direct distillation gasolines. 8. The method according to any one of paragraphs. 1 or 2, in which the distillation column is configured to function as a depentanizer or dehexanizer. 9. The method according to any one of paragraphs. 1 or 2, in which the side stream of the intermediate gasoline fraction is selected. 10. The method according to any one of paragraphs. 1 or 2, in which the pressure used in the distillation column in stage b) is equal to the pressure used in the reactor in stage a), except for the loss of feedstock in the hydraulic circuit. 11. The method according to any one of paragraphs. 1 or 2, wherein the light gasoline is subjected to a condensation and separation step to recover unused hydrogen. 12. The method of claim 11, wherein the unused hydrogen is returned to step a) or b). 13. The method according to any one of paragraphs. 1 or 2, wherein in step a), H ₂ S present in the gasoline to be treated is simultaneously added to the olefins. 14. The method according to any one of paragraphs. 1 or 2, in which the heavy gasoline fraction originating from step b) is treated in a hydrodesulfurization unit.

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