KR100813776B1 - Method for producing desulphurised petrol from a petroleum fraction containing cracked petrol - Google Patents

Abstract

The invention relates to a method for producing low-sulphur petrol from an initial petrol containing sulphur compounds comprising the following steps: a) the selective hydrogenation of the non-aromatic polyunsaturated compounds present in the initial petrol; b) increasing the molecular weight of the light sulphur products that were initially present in the petrol at the beginning of step b); c) the alkylation of at least part of the sulpur compounds present in the product resulting from step b); d) the fractionation of the petrol resulting from step c) into at least two fractions, one of said fractions being practically free of sulphur compounds and the other containing a larger proportion of sulphur compounds (heavy petrol); e) the catalytic treatment of the heavy petrol to transform the sulphur compounds in conditions that allow the, at least partial, decomposition or hydrogenation of said sulphur compounds.

Description

METHODO FOR PRODUCING DESULPHURISED PETROL FROM A PETROLEUM FRACTION CONTAINING CRACKED PETROL

The present invention relates to a process for desulfurization of gasoline obtained by conversion gasoline, in particular catalytic cracking, fluidized bed catalytic cracking (FCC), coking, bisbraking, pyrolysis. It is also possible to treat direct distillation gasoline (straight run) mixed with one or more of the above-mentioned gasolines by the process of the present invention. The method of the present invention allows obtaining high desulfurization rates while limiting octane losses due to saturation of olefins observed during hydrodesulfurization. The present invention relates to a process for the production of low sulfur gasoline (low sulfur content gasoline), comprising the steps of hydrogenation, conversion of sulfur-containing compounds, alkylation of unconverted sulfur-containing compounds, light fractions and one or more heavy Fractionating into fractions and, if desired, one or more intermediate fractions, and hydrodesulfurization of the heavy fractions and / or intermediate fractions. The process of the present invention reduces the overall sulfur content of the fraction to very low levels compatible with current or future specifications, thereby reducing the quality of the gasoline fraction, optionally including hydrocarbons with two, three or four carbon atoms. Can be improved. In addition, such desulfurization is carried out while minimizing the reduction of the octane number without appreciably reducing gasoline yield.

The production of reconstituted gasoline that meets the new environmental standards is particularly required to reduce the olefin concentrations in small amounts, but to significantly reduce the sulfur concentrations. Gasoline obtained from converting gasoline and more specifically from catalytic cracking, which can represent 30-50% of the gasoline pool, has a high olefin content and a sulfur content. The sulfur present in the reconstituted gasoline can be almost 90% and is due to catalytic cracked gasoline (FCC, “fluid catalytic cracking”, or fluid bed catalytic cracking). Therefore, desulfurization (hydrodesulfurization) of gasoline and primarily FCC gasoline is of great importance to meet product specifications.

Hydrodesulfurization of the feedstock passed to the catalytic cracking process typically produces gasoline containing 100 ppm of sulfur. However, hydrotreating units of catalytic cracking feedstocks operate under severe temperature and pressure conditions, resulting in a significant amount of hydrogen consumption and increased investment costs. In addition, all feedstock must be desulfurized, which involves the processing of very large amounts of feedstock.

Desulfurization of cracked gasoline can reduce the sulfur content of the fractions when carried out under standard conditions known to those skilled in the art. However, this method has a fatal drawback that the octane number of the fraction drops very severely, which is due to the saturation of all the olefins during hydrotreatment.

Prior art teachings have been very non-specific, and in order to obtain desulfurized gasoline that meets the standards currently enforced in terms of sulfur content and aromatics content of certain octane values and future standards that can be foreseen in 2005-2010. Many solutions have been considered. An example method is the method described in the US-A-4 131 537 patent, which says that gasoline can be fractionated into several fractions, preferably three fractions, as a function of boiling point and may be different. Conditions and the presence of a catalyst comprising at least one metal of Group VIB and / or Group VIII is described as having an advantage in desulfurizing them. This patent describes that when gasoline is fractionated into three fractions and fractions with medium boiling points are treated under mild conditions, the greatest benefit is obtained.

Another example is the EP-A-0 725 126 patent application, which contains a plurality of fractions comprising a first fraction rich in compounds that are at least easy to desulfurize gasoline and a second fraction rich in compounds that are difficult to desulfurize. A method for hydrodesulfurization of cracked gasoline is described. Before carrying out the separation, it is necessary to first determine the distribution of the sulfur-containing compound by analysis. These analyzes are necessary to select equipment and separation conditions.

In this application, the olefin content and octane number of the light cracked gasoline fraction are described as being significantly reduced when the fraction is desulfurized and desulfurized. In contrast, the fractionation of the light fractions into seven to twenty fractions, followed by analysis of the sulfur content and olefin content of these fractions, simultaneously or separately, is combined with other fractions which can be desulfurized, desulfurized or desulfurized. Determine the fraction (s) most abundant in the containing compound. This process is complex and must be performed at each change in the composition of the gasoline to be treated.

A method for hydrotreating gasoline consisting of fractionating gasoline, introducing fractions into different levels of hydrodesulfurization reactor, and converting desulfurization fractions on ZSM-5 zeolites to compensate for the octane losses recorded by isomerization are examples. For example, it is proposed in the US-A-5,290,427 patent. The isomerization is achieved by breaking down gasoline into lighter compounds.

In these methods, the gasoline to be treated generally has a starting point of 70 ° C. or higher, for example, by softening, light gasoline (a fraction corresponding to a compound having a boiling point between 70 ° C. and a C5 hydrocarbon having 5 carbon atoms). It needs to be handled separately.

According to the teachings of the US 5,599,441 patent, the desulfurization method of the naphtha fraction comprising olefinic gasoline comprises increasing the weight of the sulfur-containing compound by alkylation and then fractionating the gasoline into two fractions. Let the sulfur deficiency occur at.

According to the US Pat. No. 6,024,865, a method for producing desulfurized gasoline comprises separating gasoline into light gasoline and heavy gasoline. Light gasoline is sent to the reactor for increasing the weight of the sulfur-containing compound by alkylation. Heavy gasoline supplemented with reactive olefins is sent to the reactor to increase the weight of the sulfur-containing compound by alkylation. The heavy gasoline and light gasoline are mixed and then sent to a distillation process to recover the sulfur depleted gasoline at the top.

According to the teachings of the applicant's EP-A-1 077 247 patent, the gasoline to be desulfurized is characterized by the selective hydrogenation of the diolefinic compound (a1), optionally the molecular weight of the light sulfur-containing product present in the starting gasoline to be desulfurized. The gasoline obtained at the outlet of at least one step (a2), said steps (a1) and / or (a2) aimed at increasing, comprises a light fraction and starting gasoline which are substantially free of sulfur and contain the lightest olefins of the starting gasoline. One or more stages (b), a heavy fraction, for separation into two separate fractions comprising almost all sulfur-containing compounds present in and / or other heavy fractions containing sulfur-containing compounds from step (a2) Unsaturated sulfur-containing compounds and specifically cyclic sulfur-containing compounds present in the heavy fraction under limited hydrogenation conditions of the olefins present in the One or more steps (c) for treating the heavy fraction, which can even decompose or hydrogenate the aromatic sulfur-containing compound and an unsaturated sulfur-containing compound not converted in step (c) with limited hydrogenation of the olefin present at least one step (d) of treating gasoline derived from step (c) capable of decomposing linear and / or cyclic unsaturated sulfur-containing compounds present in the gasoline derived from (c). This method can be applied to result in temperature limitations at the top of the fractionation column to obtain a top fraction that is substantially free of sulfur and in particular free of thiophene. Thus, this restriction is generally not beneficial when considering the use of the overall method, since the fraction recoverable at the top of the fractionation column is limited in temperature and amount, which is treated again, hoping to reduce its sulfur content. Because you have to.

The present invention can produce desulfurized gasoline while limiting octane loss due to desulfurization. The process of the present invention is distinguished from standard desulfurization processes based on desulfurization of the entire gasoline. In some cases, these methods provide separation of two or more fractions of gasoline: one fraction containing light gasoline and one fraction containing heavy fraction, ie, gasoline with a final boiling point higher than the boiling point of light gasoline.

Heavy gasoline is desulfurized, for example, by treatment with hydrogen or absorption of sulfur-containing compounds. Processes involving hydrotreating lead to significant saturation of the olefins, resulting in high octane losses.

Light gasoline is subjected to hydrodesulfurization under mild conditions, washing with basic solutions or adsorption on solids, or by softening by oxidation methods such as METOX® of the Universal Oil Products (UOP) Company, which may be extractable for example. May be desulfurized.

Some methods can only desulfurize heavy gasoline, i.e. sulfur-containing compounds that are normally present in light gasoline (mercaptans) that are weighted upstream from the distillation zone or fractionation zone (splitter) first.

As long as the methods for increasing the weight of sulfur-containing compounds by the alkylation set forth herein are contemplated, sulfur-containing compounds and heavy sulfur- wherein light gasoline is increased by alkylation by making desulfurized light gasoline using these methods It is possible to concentrate the containing compound. Thus, these methods cannot desulfurize the overall conversion gasoline fraction, and in particular cannot desulfurize fractions obtained from catalytic cracking units. In addition, the weight-increasing method of sulfur-containing compounds by alkylation is based on acid catalysis. The service life of the catalyst may be limited by diolefinic compounds and basic compounds (mainly nitrogen-containing compounds) in the gasoline to be treated.

1 is a diagram schematically illustrating an embodiment of the present invention in a non-limiting manner.

Gasoline α containing sulfur-containing compounds, diolefins and olefins is injected in line (1). Hydrogen is injected into line 2, with an amount such that the hydrogen / diolefin molar ratio is at least one. Gasoline and hydrogen are brought into contact in reactor A for the selective hydrogenation of the diolefin under optimized conditions that hydrogenate the diolefin while limiting the saturation of the olefin.

The effluent of reactor A is sent by line 3 to unit B for increasing the weight of the sulfur-containing compound. The reaction carried out in reactor (B) is essentially a reaction for increasing the weight of mercaptans having 1 to 6 carbon atoms as well as sulfides having 2 to 6 carbon atoms. In addition, partial conversion of compounds such as CS2 and COS is also observed. The resulting gasoline is introduced into reactor C by line 4 to increase the weight of the sulfur-containing compound by addition to the olefins. Sulfur-containing compounds of which weight is mainly increased in this reactor are thiophene-based compounds. Also in this reactor (C), oligomerization of olefins and partial alkylation of benzene compounds are observed. The gasoline produced in this reactor (C) is heavier than gasoline (α) and lacks a light sulfur-containing compound. The gasoline produced in the reactor (C) is injected into the fractionation column (D) via line (5), where the gasoline is separated into two or more fractions.

Light gasoline, which may have an end point of 55 ° C. to 160 ° C., is recovered at the top of the column. This gasoline is desulfurized and no further treatment is necessary. The final temperature of the light gasoline is determined by the maximum amount of sulfur allowed.

The heavy gasoline recovered at the bottom of the column by line 7 is mixed with the hydrogen injected by line 8 and then sent to the desulfurization fraction (E + F). This gasoline has a distillation starting point between 50 ° C and 130 ° C.

The hydrodesulfurization section (E + F) is designed to desulfurize gasoline while limiting the hydrogenation of olefins, which can limit octane losses. It consists of two or more reactors in series, the first (E) comprising an optimized catalyst system for saturating thiophene-based compounds and partially converting sulfur-containing compounds to H ₂ S. The second contains a catalyst, which is optimized for converting mercaptans to H ₂ S by limiting the hydrogenation of olefins present in gasoline. This desulfurization method is described in the EP 1 077 247 patent application.

Heavy gasoline recovered by line 10 and light gasoline recovered by line 6 may be mixed to produce fully desulfurized gasoline recovered by line 11.

Summary of the Invention

The present invention relates to a process for producing low sulfur gasoline, wherein using the process of the present invention the entire gasoline fraction containing sulfur, preferably catalytic cracking or coking or pyrolysis, or bis The gasoline fraction of breaking, if necessary, can improve the quality of the gasoline fraction mixed with distilled gasoline directly, and without compromising the gasoline yield, while minimizing the reduction of octane number due to hydrogenation of olefins. The sulfur content of the fraction can be reduced to very low levels. In addition, the feedstock according to the process of the present invention comprises an additional gasoline fraction, wherein the C4 fraction may comprise a hydrocarbon having 2, 3 or 4 carbon atoms.

The present invention provides a process for producing low sulfur gasoline from a starting gasoline containing at least 150 parts per million (ppm), often at least 200 ppm and generally at least 300 ppm, of sulfur-containing compounds by weight, the method comprising at least the following steps: Manufacturing method:

Step (a) for selective hydrogenation of non-aromatic polyunsaturated compounds present in the starting gasoline;

Sulfur-containing products, mainly in the form of mercaptans having 1 to 6 carbon atoms in the molecule and in the form of sulfides having 2 to 6 carbon atoms in the molecule initially present in the gasoline introduced in step (a) And / or at least one step (b) aimed at increasing the molecular weight of the light sulfur-containing product which is a sulfur-containing product contained in the product from step (a);

At least one step for alkylating at least a portion of the sulfur-containing compound in the form of a thiophene-based compound present in the product derived from step (b) aimed at obtaining a sulfur-containing compound having a primarily higher molecular weight (c) );

The gasoline from step (c) is divided into two or more fractions, i.e., the first fraction (light gasoline) which is substantially free of sulfur and which contains the lightest olefins of the unconverted starting gasoline of step (c); One or more other fractions which are heavier and richer in sulfur-containing compounds and preferably so-called heavy fractions (heavy gasoline) containing most of the sulfur-containing compounds present in the gasoline derived from step (c). Step (d) or more; And

At least one step (e) for treating at least one heavier fraction derived from step (d) on a catalyst capable of at least partially decomposing a sulfur-containing compound. During this step (e), it is preferred that the so-called heavy fraction separated in step (d) is treated.

The term "mainly" as used in steps (b) and (c) means that at least 50% of the sulfur-containing compound in the form of a compound of the type indicated during the given step is converted.

Often, step (e) is for treating one or more of the heaviest fractions separated in step (d) on a catalyst capable of at least partially decomposing a sulfur-containing compound, wherein hydrogenation of the olefins on the catalyst is limited. Under conditions.

According to a preferred embodiment of the invention, the treatment of one or more heavier fractions, preferably heavy gasoline derived from step (d), is carried out in two steps:

(E) treating at least one heavier fraction and preferably heavy gasoline on said catalyst, under conditions in which hydrogenation of olefins is limited on a catalyst capable of at least partially decomposing sulfur-containing compounds; And

Unsaturated sulfur-containing compounds which are at least partially decomposed during step (e) with limited hydrogenation of olefins, preferably unconverted during step (e) with limited hydrogenation of olefins And at least one step for treating the product obtained in step (e) under conditions capable of degrading the linear and / or cyclic saturated sulfur-containing compounds and without removing H ₂ S formed in step (e) on the catalyst. (f).

The term "polyunsaturated compound" in the sense of this technology is meant to include diolefin-based hydrocarbon-containing compounds containing two double bonds, which hydrocarbon-containing compounds contain two or more double bonds, but are not aromatic. The hydrocarbon-containing compound contains one or more triple bonds and is present in the starting gasoline. As a rule, the starting gasoline contains essentially diolefinic compounds as polyunsaturated compounds. In the sense of this technique, the low sulfur gasoline obtained contains less than 150 ppm by weight, often less than 100 ppm by weight and generally less than 80 ppm by weight of sulfur.

Step (b) for the conversion of light sulfur-containing compounds relates to the conversion of saturated sulfur-containing compounds having a boiling point below 120 ° C. This step can be carried out simultaneously with step (a) for all or part of the starting gasoline in the same reactor or in different reactors as required. It may also be carried out separately for all or part of the hydrogenated gasoline in step (a). In step (b), the thiophene and thiophene compounds are hardly converted. Step (a) for the hydrogenation of unsaturated compounds and step (b) aimed at increasing the molecular weight of the saturated light sulfur-containing product initially present in the gasoline introduced in step (a) are carried out as a single catalyst, if necessary. It may be performed simultaneously in a single reaction zone containing one or more layers made up.

Step (c) is generally a step for alkylating sulfur-containing compounds belonging to the group comprising mercaptans, thiophenes and thiophene-based compounds present in the product from step (b). The optionally present mercaptan is one formed in step (a) and / or step (b) or present in the starting gasoline and not converted in step (a) and / or step (b). This step can be carried out in one or more reactors connected in series or in parallel. In the case of a device comprising several reactors connected in series, the first reactor can serve as a guard bed to hold the basic compound optionally present in the starting gasoline. In addition, these basic compounds must be at least partially removed before introducing gasoline into step (a) for hydrogenation of the polyunsaturated compound. This removal is preferably carried out by treatment with an aqueous acid solution. The operating conditions can be adjusted such that a portion of the starting gasoline olefins are converted to branched long olefins by the addition reaction between the olefins. In addition, the operating conditions can be adjusted such that a portion of the aromatic compound increases in weight by alkylation of the olefin.

Step (d) for fractionating gasoline obtained at the end of step (c) comprises fractionating at least two fractions: preferably a light that is substantially free of sulfur and contains the lightest olefins of the starting gasoline. Fractions, and preferably heavy fractions (gasoline or heavy fractions) initially present in the starting material and / or enriched in most of the sulfur-containing compounds formed during steps (a), (b) and (c). It is also possible to separate the gasoline obtained in step (c) into two or more fractions, for example a light fraction, one or more intermediate fractions and a heavy fraction. In this case, the intermediate fraction (s) can generally be sent to the catalyst reforming unit after the concentrated desulfurization step.

Step (e) for treating the intermediate fraction containing a portion of the sulfur-containing compound that is significantly larger than that contained in the heavy gasoline and / or light fraction comprises sulfur-containing compounds, specifically cyclic sulfur-containing compounds and even A step for treating said fraction on said catalyst by placing it under conditions that limit hydrogenation of olefins on a catalyst capable of at least partially decomposing aromatic compounds, such as thiophene-based compounds.

Step (f) at least partially decomposes or hydrogenates the sulfur-containing compound that is not converted in step (e) with limited hydrogenation of the olefin, preferably linear with the unsaturated sulfur-containing compound and unconverted in step (e). And / or obtained in step (e) without removing the H ₂ S formed in step (e) on the catalyst and under conditions capable of decomposing or hydrogenating the cyclic saturated sulfur-containing compound and specifically the thiophene-based compound and mercaptan. Step for treating the product.

Steps (e) and (f) are generally carried out in at least two consecutive separate reaction zones. The catalytic treatment carried out in steps (e) and (f) can be carried out in a single reactor containing two catalysts or in two or more different reactors. When the treatment is carried out using two reactors, the two reactors are connected in series so that the second reactor is preferably treated with effluent at the outlet of the first reactor as a whole, between the first reactor and the second reactor. It is more preferable to treat the liquid and the gas without separating them. It is also possible to connect several reactors in parallel or in series for one and / or the other of step (e) and / or step (f).

Furthermore, it is not necessary to remove the H ₂ S formed during step (e) prior to transferring the effluent from step (e) to the inlet of the hydrogenation reactor (s) of step (f).

Thus, one of the advantages of the process according to the invention is based on the fact that there is no need to adjust the H ₂ S content between step (e) and step (f).

It is also preferred that step (g) be carried out after step (f), which comprises the light gasoline separated in step (d) and the light gasoline derived from step (f) for forming any total desulfurized gasoline. Mixing at least a portion of the mixture.

The total desulfurized heavy gasoline derived from step (f) is preferably mixed with the light gasoline derived from step (d) without separating the liquid and gas contained in the light gasoline after desulfurization; Residual sulfur-containing compounds relative to the content of sulfur-containing compounds in heavy gasoline that has been extensively desulfurized, ie heavy gasoline exiting step (d), by carrying out a simple stripping with one or more cover gases as necessary. It is possible to remove H ₂ S of heavy gasoline containing less than 50% by weight and often less than 20% by weight.

In some specific examples, the quality improvement of light gasoline and desulfurized heavy gasoline is performed separately. Therefore, it is not necessary to perform step (g).

For gasoline with a final boiling point of 130 ° C. or higher, two additional steps may be necessary:

An additional step for the removal of the basic compound, which may be carried out by washing with an aqueous acid solution to remove the basic compound, may be necessary before step (c).

-Fractionation of gasoline derived from step (d) for fractionation or other treatment of step (e) or (f) for hydrodesulfurization to be separated from gasoline, heavy fraction having a starting point, for example 210 ° C. And a lighter fraction where the end point is for example 210 ° C. If the fractionation is performed on gasoline derived from step (d), the light fraction is transferred to step (e).

The feedstock of the process according to the invention comprises a gasoline fraction containing sulfur, preferably a gasoline fraction derived from a cracking unit, a hydrocarbon (C2 or C3) having a broad boiling range of approximately 2 or 3 carbon atoms. More preferably 5 carbons ranging from boiling point to about 250 ° C. or less, preferably ranging from approximately boiling point of hydrocarbons having two or three carbon atoms (C 2 or C 3) to about 220 ° C. or less Gasoline fractions derived from catalytic cracking units ranging from the approximate boiling point of hydrocarbons (C5) having atoms to about 220 ° C. or less. The process of the present invention is particularly applicable to catalytic cracked gasoline with a final boiling point of about 120 ° C to about 230 ° C.

The advantages of the method of the present invention over the prior art methods are as follows:

1. Formation of the sulfur in the gasoline as well as the removal of the diene compound and optionally the acetylene compound contained in the starting gasoline, wishing to limit the deactivation of the alkylation catalyst of step (c) of the sulfur-containing compound.

2. Removal of light mercaptans to produce soft light gasoline that does not require purification or subsequent desulfurization.

3. Increased desulfurized light gasoline production recovered at the top of the fractionation column, causing a decrease in the amount of gasoline to be treated by hydrodesulfurization.

4. Fractionation of branched olefin-rich heavy gasoline where octane is not very sensitive to saturation of olefins.

5. Selective desulfurization of heavy gasoline (or as a result of lateral emissions) limiting saturation of olefins and octane losses in heavy gasoline.

6. Overall reduction in the vapor pressure of the produced gasoline compared to the starting gasoline.

Detailed description of the invention

The present invention relates to a process for obtaining desulfurized gasoline having a limited sulfur content from converted gasoline and preferably gasoline derived from units for catalytic cracking, coking, visbreaking or pyrolysis mixed with saturated gasoline as needed. This process first carries out the selective hydrogenation of the diolefins to gasoline, and then 1 to 6 in the molecule which has to be identified in the light gasoline after fractionation so that they are essentially in the heavy fraction after the fractionation step according to the invention. For the conversion of sulfur containing compounds in the form of mercaptans with two carbon atoms and gasoline in the form of sulfides with two to six carbon atoms, for the conversion of sulfur-containing compounds in the form of mercaptans and sulfides Present in the form of a thiophene-based compound in the gasoline derived from the step. And it performs the steps for the alkylation of a compound containing sulfur. In this step, the operating conditions can be adjusted to promote the alkylation reaction of the olefins, particularly with respect to the olefins and aromatic compounds which cause a decrease in the vapor pressure of gasoline. One or more fractions, preferably heavy fractions or intermediate fractions, derived from the fractionation step can be treated in the step of converting these sulfur-containing compounds to H ₂ S (hydrogen sulfide) with or without reducing the saturation of the olefins. .

After this fractionation, the heavy gasoline or one or more intermediate fractions are treated in the hydrodesulfurization zone, preferably in the presence of a hydrodesulfurization catalyst or an absorbent if necessary. In the process according to the invention it is preferred that the desulfurization of the light fraction is unnecessary, because the bulk of the sulfur-containing compounds initially present in the gasoline is present in the heavy fraction and the hydrogenation, conversion of the sulfur-containing compounds as necessary (step ( b)) in step (a) and step (b) by alkylation (step (c)) of the thiophene-based compound and any mercaptan, specifically at least a portion of the unconverted sulfur-containing compound in step (b) Because it is present in the intermediate fraction (s) of fractionation step (d) which is carried out after the step for conversion of residual mercaptan which is not converted and / or formed.

With this method it is possible to obtain good quality desulfurized gasoline which does not result in significant decrease in olefin content or octane number despite high desulfurization rate; There is no need to treat light gasoline by the hydrodesulfurization zone or softening zone or readjustment in such a way as to recover the octane number of gasoline. Due to this method, a significant desulfurization rate is obtained under ideal operating conditions described later.

The sulfur-containing radicals contained in the feedstock treated by the process of the present invention may be used for example mercaptans, sulfides, disulfides and / or heterocyclic compounds, for example thiophenes or alkyl-thiophenes or heavier compounds, for example Benzothiophene and / or dibenzothiophene.

The fractionation point of gasoline is preferably limited to prevent the presence of sulfur-containing compounds in light gasoline. In the absence of a reactor for alkylation of sulfur-containing compounds, only a small amount of C6 olefins and C5 olefins can be separated in light gasoline, fearing that too many thiophene fractions will be mixed into the fractions. Thus, the process according to the invention can be carried out using thiophene and more generally thiophene-based compounds using, for example, an alkylation zone located upstream from a fractionation zone or a fractionation zone integrated within said zone, according to the detailed embodiments described below. It is beneficial to follow the steps for the transition.

Separation of light sulfur-containing compounds, usually present in the form of mercaptans and sulfides with 2 to 6 carbon atoms in the molecule, to recover larger fractions of light gasoline while limiting the sulfur content of the fraction without further treatment. It is preferred to treat the feedstock in step (b) on a catalyst and under conditions that can later be converted to sulfur-containing compounds with higher boiling points, optionally identified in one or more intermediate fractions or heavy gasoline. These intermediate and / or heavy fractions may be desulfurized. This desulfurization is carried out under definite conditions and can lead to high desulfurization rates, with hydrodesulfurization catalysts capable of limiting saturation of the olefins as needed, or limiting the hydrogenation rate of the olefins and thus the octane losses according to a preferred embodiment of the invention. It is carried out by a catalyst of any configuration possible.

The sulfur content of the gasoline fraction produced by catalytic cracking and specifically fluidized bed catalytic cracking (FCC) depends on the sulfur content of the feedstock treated by the FCC, the presence or absence of feedstock pretreatment of the FCC, as well as the end point of the fraction. In general, the sulfur content of the entire gasoline fraction, specifically the gasoline fraction obtained from the FCC, is at least 150 ppm by weight and generally at least 500 ppm by weight. For gasoline with an end point of 200 ° C. or higher, the sulfur content is often at least 1,000 ppm by weight, which in some cases amounts to about 4,000 to 5,000 ppm.

The process of the present invention provides that when high desulfurization rates of gasoline are required, i.e., desulfurization gasoline is 10% or less of sulfur of the starting gasoline, if necessary, 5% or less, even 2% or less (these desulfurization rates are each 90% or more, Especially at least 95% or at least 98%).

The process according to the invention comprises at least the following steps (a) to (e):

Step (a) for the selective hydrogenation of the diolefin: This step removes the diolefin which may lead to preliminary deactivation of the catalyst to increase the weight of the sulfur-containing compound by alkylation during step (c) described below. It is for forming a gum in desulfurized gasoline. This step is carried out by passing the effluent, preferably the effluent consisting of the entire gasoline fraction, over a catalyst capable of selectively hydrogenating the diolefin of gasoline without hydrogenating the olefin.

Step (b) for increasing the weight of mercaptan and light sulfide on a supported metal catalyst: This reaction can be carried out in a reactor for the selective hydrogenation of diolefins. This stage comprises light or sulfur-containing by reacting all or a portion of the starting gasoline or gasoline hydrogenated in step (a), preferably all of the starting gasoline or gasoline hydrogenated in step (a) with all or a portion of the olefins. Developing at least a portion of the compound (eg, ethyl mercaptan, propyl mercaptan) onto a catalyst capable of converting it to a heavier sulfur-containing compound. This step is for example a catalyst capable of hydrogenating the diolefin and converting the light sulfur containing compound into a heavier sulfur-containing compound, preferably together with the olefin, or used to carry out step (a) above. It is carried out concurrently with step (a) by deploying the starting gasoline onto a separate catalyst capable of carrying out the conversion in the same reactor as the one.

Step (c) for increasing the weight of the sulfur-containing compound by alkylation: This step can remove most of the sulfur-containing compound present in the form of a thiophene-based compound by an addition reaction to the olefin. This step carries out the addition of all or part of the gasoline obtained from step (b) to the olefins with sulfur-containing compounds in the form of mercaptans and sulfides, and the alkylation of thiophene and thiophene derivatives with these same olefins. Developing onto a catalyst having an acid action which can be carried out.

Step (d) for fractionation of gasoline obtained at the end of step (c): This step is for producing light desulfurized gasoline at the top of the distillation column. The gasoline thus recovered is low in sulfur and usually does not require further treatment. The light gasoline with a low sulfur content is usually transferred directly to the storage zone of the gasoline (sometimes referred to in the art as a gasoline pool), which preferably does not require further aftertreatment. Gasoline recovered at the bottom of the column concentrates sulfur-containing compounds initially present in the feedstock. This column may comprise, for example, side discharges which may obtain one or more intermediate fractions.

In step (e), the gasoline at the bottom of the column and / or the gasoline contained in the intermediate fraction from step (d) is desulfurized by hydrotreating.

According to a preferred embodiment of the present invention, the gasoline at the bottom of the column and / or the gasoline contained in the intermediate fraction derived from step (d) are subjected to the conditions under which step (e) causes olefin saturation to partially limit octane loss and Desulfurized on the catalyst.

According to a more preferred embodiment of the invention, in continuous steps (e) and (f), the gasoline at the bottom of the column and / or the gasoline contained in the intermediate fraction from step (d) may limit the saturation of the olefins. Desulfurization by hydrotreating according to the present method. In practice, the implementation of selective hydrodesulfurization limits the saturation of the olefins, thus limiting the octane loss of gasoline. Such desulfurized heavy gasoline and / or one or more intermediate gasoline can be stripped as needed (ie, a gas stream containing one or more cover gases is developed through the gasoline), thus optionally generated during the desulfurization process. Remove H ₂ S.

According to a variant of the process of the invention, it is possible to combine one or more reaction zones and a fractionation column. The reaction zone (s) are operated on one or more fractions sampled inside the fractionation column and the effluent from the reaction zone is sent to the fractionation column. Thus, the reaction zone (s) connected to the fractionation column of step (d) may be selected from the group consisting of the reaction zones of the following steps:

Conversion of sulfur-containing compounds such as thiophene, thiophene-based compounds and optionally mercaptans by alkylation (step (c))

Desulfurization of the intermediate fraction and / or desulfurization of the heavy fraction (step (e) and / or step (f)).

A device as described above comprising a fractionation column in combination with an external reactor that can be used in the process of the present invention is described, for example, in the US 5,177,283 patent, US 5,817,227 patent and US 5,888,355 patent and in the oil and petrochemical fields. Applicable

According to another method variant of the process of the invention, one or more reaction zones (reaction zones present inside the column) in the fractionation column are preferably reactive instead of the fractionation column in order to be placed in a zone where the reagent concentration is at its maximum. Columns can be used. Thus, in the case of step (c) for converting sulfur-containing compounds, for example thiophene-based compounds by alkylation, it will be preferred that the reaction zone is located in a zone representing the maximum concentration of these compounds.

According to a preferred variant of the process of the invention, the reaction zone present inside the column is selected from the group consisting of the following reaction zones: thiophene, thiophene-based compound and optionally mercaptan by alkylation. Conversion of sulfur-containing compounds such as (step (c)), desulfurization of the middle fraction and / or desulfurization of the heavy fraction (step (e) and / or step (f)).

In a very preferred embodiment according to the invention, the reaction zone is located in the middle of the fractionation column, which may constitute a compound having a moderate boiling point, for example a compound which may constitute an intermediate fraction and only at the bottom of the column at the end of the fractionation step. The compound recovered with or with the heavy fractions is treated. The heavy fraction is then processed in an external reactor which may or may not be combined with a fractionation column.

Such reactive columns are known to those skilled in the art and are described, for example, in patents or patent applications such as US 5,368,691, US 5,523,062, FR 2,737,131, FR 2,737,132 and EP-A-0 461 855.

Another variation of the method according to the method of the invention involves the use of both at least one reactive column and an external reactor which may or may not be connected to said column. Such a variant method is described, for example, in the WO 00/15319 patent application.

The above modification methods illustrate possible modifications of the method of the present invention. Indeed, the process according to the invention is combined with the fractionation column of step (d) or outside of the column and in that the effluent of the reaction zone (s) is not recycled to the fractionation column. It can be carried out by combining the reaction zones (step (a), step (b), step (c), step (e) or step (f)) that is not connected with.

One of the advantages of the process according to the invention is largely based on the fact that it is not necessary to desulfurize the light fraction of gasoline derived from fractionation. The conversion of sulfur-containing compounds and / or thiophene-based compounds (steps (b) and / or step (c)) can actually significantly reduce the content of sulfur-containing compounds in the light fraction and any one or more intermediate fractions. In general, bulk of these compounds can be recovered in the heavy fraction and optionally in the intermediate fraction (s).

Steps (b) and (c) are generally less than 60% by weight of the thiophene-based compound and even less than 40% by weight in step (b), while the conversion is generally at least 80% by weight in step (c), Preferably at least 90% by weight, very preferably at least 95% by weight. In practice step (b) essentially makes mercaptans and light sulfides heavier, while step (c) essentially makes the thiophene-based compounds heavier.

The operation is carried out while maintaining the olefin bulk in the light fraction and, if desired, in one or more intermediate fractions that do not require concentrated desulfurization. The content of the sulfur-containing compound of the light fraction thus obtained is generally less than 100 ppm, preferably less than 50 ppm, more preferably less than 20 ppm and very preferably less than 10 ppm.

Another advantage is based on the fact that the residual content of the sulfur-containing compounds of the gasoline desulfurized by the process of the invention is particularly low and the octane number of gasoline is maintained at high levels.

Hereinafter, the method according to the present invention will be described in detail.

Hydrogenation of Diolefin (Step (a)):

Hydrogenation of the diene is a step that can remove almost all of the dienes present in the gasoline fraction containing sulfur to be treated prior to hydrodesulfurization. This preferably takes place in the first step (step (a)) of the process of the invention and is generally carried out in the presence of a metal and a substrate selected from the group consisting of at least one Group VIII metal, preferably platinum, palladium and nickel. do. For example, it is possible to use nickel-based or palladium-based catalysts deposited on inert substrates such as alumina, silica or substrates containing at least 50% alumina.

A pressure suitable for maintaining at least 60%, preferably at least 80%, more preferably at least 95% by weight of the liquid gasoline to be treated in the reactor is used; It is generally about 0.4 to about 5 MPa, preferably at least 1 MPa, more preferably 1 to 4 MPa. The hourly volume flow rate of the liquid to be treated is about 1 to about 20 h ⁻¹ (volume of feedstock per hour per catalyst volume), preferably 2 to 10 h ⁻¹ , very preferably 3 to 8 h ⁻¹ . The temperature is most generally about 50 to about 250 ° C, preferably 80 to 220 ° C, more preferably 100 to 200 ° C. It is very preferred that the temperature be limited to 180 ° C. The hydrogen to feedstock ratio expressed in liters is generally 1 to 50 liters per liter, preferably 2 to 30 liters per liter, more preferably 3 to 25 liters per liter.

The choice of operating conditions is particularly important. The operation will most commonly be carried out in the presence and pressure of an amount of hydrogen that slightly exceeds the stoichiometric value needed to hydrogenate the diolefin. Hydrogen and the feedstock to be treated are preferably injected upwards or downwards in a reactor comprising a fixed catalyst bed.

Other metals may be combined with the main metals to form a bimetallic catalyst, examples of which are molybdenum or tungsten. The use of such a catalyst formula is claimed as a right, for example, in the FR 2 764 299 patent.

Catalytic cracked gasoline may contain up to several percent by weight of diolefin. After hydrogenation, the diolefin content is generally reduced to less than 3,000 ppm, even less than 2,500 ppm, more preferably less than 1,500 ppm. In some cases, less than 500 ppm can be obtained. The diene content after selective hydrogenation can be reduced even below 250 ppm, if desired.

According to a specific embodiment of the process according to the invention, the hydrogenation step of the diene takes place in a catalytic hydrogenation reactor comprising the amount of hydrogen needed to carry out the desired reaction and a catalytic reaction zone across all feedstocks.

Conversion of Light Sulfur Compounds (Step (b)):

This step converts the light sulfur compound, ie the compound identified at the end of step (a) for hydrogenation of the diene in the light gasoline (after fractionation in step (d)), to a heavier sulfur-containing compound mixed into the heavy gasoline. It includes the process of making. The light sulfur-containing compound is selected from mercaptan family with 1 to 6 carbon atoms and sulfide family with 2 to 6 carbon atoms. The conversion is preferably carried out on a catalyst comprising at least one Group VIII element of the Periodic Table (Handbook of Chemistry and Physics 45th Edition 1964-1965; Groups 8, 9 and 10 of the new Periodic Table). The choice of catalyst is carried out in order to facilitate the reaction between the light mercaptan and the olefin, in particular producing heavier sulfides or mercaptans. In addition, other compounds such as COS or CS2 can also be converted as needed.

If necessary, this step may be performed simultaneously with step (a). For example, it is particularly advantageous to operate under conditions that allow at least a portion of the mercaptan form of the compound to be converted during the hydrogenation of the diolefin. This substantially reduces the mercaptan content. For this purpose, the hydrogenation of dienes described in the EP-A-0 832 958 patent application can be used, which advantageously utilizes the catalyst or palladium-based catalyst described in the FR 2 720 754 patent.

Another possibility is to use a nickel-based catalyst identical or different from the catalyst of step (a), for example the catalyst recommended in the process of the US-A-3 691 066 patent, thereby making the mercaptan (butyl mercaptan) heavier. Can be converted to a sulfur-containing compound (sulfide).

Another possibility for carrying out this step involves at least partially hydrogenating thiophene to thiophan (boiling point 121 ° C.) with a boiling point greater than the thiophene boiling point. This step can be carried out on a catalyst with a nickel, platinum or palladium base. In this case, the temperature is generally 100 to 300 ° C, preferably 150 to 250 ° C. The H ₂ / feedstock ratio can be adjusted to 1 to 20 liters per liter, preferably 3 to 15 liters per liter, to facilitate the desired hydrogenation of thiophene-based compounds, if possible, and to reduce the hydrogenation of olefins present in the feedstock. have. The volume flow rate is generally 1 to 10 h ⁻¹ , preferably 2 to 4 h ⁻¹ and the pressure is 0.5 to 5 MPa, preferably 1 to 3 MPa.

Conversion of sulfur-containing compound by alkylation (step (c)):

This step is carried out from step (b) onto a catalyst having an acid action capable of adding sulfur-containing compounds in the mercaptan form onto the olefins or carrying out the alkylation of thiophene and thiophene derivatives with these same olefins. It is preferable to include the process of developing the whole fraction derived. The operating conditions can be adjusted to carry out certain conversions in which the conversion of the thiophene and / or thiophene-based compound is at least 80% by weight, preferably at least 90% by weight, very preferably at least 95% by weight. In addition, other compounds, such as COS or CS2, may also be converted as needed.

During this step, a portion of the olefins in the starting gasoline can be converted to branched long olefins by addition reaction between the olefins (oligomerization), and a portion of the aromatic compounds are increased in weight by alkylation with the olefins.

In order to reduce the oligomerization activity of the acid catalyst used as necessary, gasoline can be supplemented with a compound known to inhibit the oligomerization activity of the acid catalyst, for example alcohol, ether or water.

During alkylation, thiophene-based compounds having a boiling point of about 60 ° C. to about 160 ° C. react with olefins at a conversion rate of at least 80% by weight, preferably at least 90% by weight, with a boiling point significantly higher than that of the starting thiophene compound. It will form offene alkyl.

In addition, all or part of the benzene can be removed by alkylation with olefins.

These compounds of higher molecular weight are mainly characterized by higher boiling points than they had before alkylation. Thus, the theoretical boiling point of thiophene at 84 ° C. moves up to 150 ° C. for thiophene alkyl. This reaction is generally linked to the olefin addition reaction which results in an increase in the weight of the gasoline, in particular when the gasoline fraction and / or the starting gasoline is light, and to its vapor pressure decrease.

This alkylation step is carried out in the presence of an acid catalyst. This catalyst can equally be a resin, zeolite, clay, any silica functionalized or any silico-aluminate having an acid, or any grafted substrate of acid functionality. The ratio of injected raw material volume to catalyst volume is 0.1 to 10 liters / liter / hour and preferably 0.5 to 4 liters / liter / hour. More specifically, this alkylation step is carried out on one or more oxides such as alumina (gamma, delta, eta form, alone or mixed), silica, alumina silica, titanium silica, zirconium silica or any other solid with any acid. For example, silica, alumina or alumina silica, silicoaluminates, titanosilicates, mixed alumina-titanium compounds, clays, resins, of one or more elements such as (titanium, zirconium, silicon, germanium, tin, tantalum, niobium ... A group consisting of bronzed acid (including phosphoric acid, sulfuric acid, boric acid, hydrochloric acid) supported on a mixed oxide obtained by grafting one or more organometallic compounds (selected from the group consisting of alkyl and / or alkoxy metals) It is carried out in the presence of at least one acid catalyst selected from. Certain embodiments of the present invention utilize a physical mixture of two or more of said catalysts having a ratio of 95/5 to 5/95, preferably 85/15 to 15/85, very preferably 70/30 to 30/70. Process may be included.

The temperature of this step is generally about 10 to about 350 ° C., depending on the type of catalyst and the acidity. Thus, for supported phosphoric acid type catalysts, the temperature is generally about 50 to about 250 ° C, preferably about 100 to about 210 ° C.

The molar ratio of olefin to thiophene-based compound is at least 10 mol / mol, preferably at least 100 mol / mol.

The operating pressure of this stage is generally from 0.1 to 3 MPa, preferably the pressure at which the feedstock is in liquid form under said temperature pressure conditions, or a pressure higher than 0.5 MPa.

At least a portion and preferably all of the effluent from step (c) for the conversion of the sulfur-containing compound are sent to a fractionating unit (step (d)) which is to be separated into two or more fractions: preferably continuous desulfurization is carried out. Light fraction and heavy fraction which are conveyed after mixing with the intermediate fraction as necessary as a whole into the desulfurization zone operating in one step (step (e)) or in two steps (step (e) and step (f)).

Separation of two or more fractions of gasoline from step (c) (step (d)):

According to a first variant of the process of the invention, the gasoline is fractionated into two fractions:

A light fraction containing a limited residual sulfur content, preferably less than about 100 ppm, very preferably less than about 20 ppm, and which can be used without performing other treatments for the purpose of generally reducing its sulfur content,

A heavy fraction in which the bulk of sulfur initially present in the feedstock is preferably concentrated.

This separation is preferably carried out by a standard distillation column, also called a splitter. This fractionation column is capable of separating the light fraction of gasoline containing the small fraction of sulfur and preferably the heavy fraction containing the sulfur bulk initially present in the starting gasoline.

The column is usually operated at a pressure of 0.1 to 2 MPa and preferably 0.2 to 1 MPa. The theoretical number of plates of the separation column is generally from 10 to 100 and preferably from 20 to 60. The reflux rate, expressed as the ratio of the liquid flow rate in the column divided by the distillate flow rate expressed in kg / h, is generally less than 1 unit, preferably less than 0.8.

The light gasoline obtained at the end of the separation generally consists of hydrocarbon-containing fractions having 5, 6 and 7 carbons. In general, this light fraction has a low sulfur content. In other words, the light fraction does not need to be treated before the light fraction is used as fuel.

In this case, gasoline is preferably fractionated into two or more fractions having the following characteristics:

So-called hard fraction (fraction L), preferably having a boiling point below about 120 ° C. This temperature is given by way of example; This generally corresponds to a maximum temperature of less than 20 ppm sulfur content.

At least one so-called heavy fraction (fraction H) with a boiling point higher than about 100 ° C.

The light fraction L is injected into a gas-liquid separation flask to separate the unconsumed hydrogen and the H ₂ S formed in steps (a) and / or (b) and / or (c) to generally yield 5 to 7 olefins. It has two carbon atoms.

The so-called heavy fraction H1, ie the fraction whose temperature is higher than about 100 ° C., is transferred to step (e) and preferably to the desulfurization zone of steps (e) and (f).

According to a second variant of the process of the invention, the gasoline is fractionated into three or more fractions: light fraction, heavy fraction and one or more intermediate fractions.

The hard fraction is the same as described above. For example, an intermediate fraction I2 having a boiling point of at least 100 ° C. and at most 140 ° C. and even about 160 ° C. is treated in step (e) of the process of the invention and then, if necessary, in step (f) of the process of the invention. do. The heavy fraction H2 is then a fraction having a boiling point of generally about 160 ° C. or higher or about 140 ° C. In this case, the unit of the intermediate fraction + heavy fraction is the same as the heavy fraction H1 when the fractionation is limited to two fractions.

Heavy fraction H2 having a boiling point of generally about 160 ° C. or above about 140 ° C. is transferred to the desulfurization zone.

In another variant of the process of the invention, it is possible to fractionate the product from step (c) into three or more fractions: a light fraction (L) exhibiting the properties as described above, one or more intermediate fractions (I2) And one or more heavy fractions (H2).

Intermediate fraction I2 having a boiling point of about 100 ° C. to about 120 ° C. or about 160 ° C. is either transferred to the conversion unit of the sulfur-containing compound according to step (c) or recycled in step (c).

After step (d), fraction (s) I2 is again partitioned into intermediate fraction I3 and heavy fraction H3. The fraction H3 thus obtained is mixed with fraction H2 if necessary, preferably before desulfurization, and fraction I3 is transferred into a unit for the conversion of sulfur-containing compounds according to step (c) or in step (c) Can be recycled.

In the following description, the conditions provided for step (e) refer to the conditions under which a single desulfurization step is carried out and the conditions of a preferred embodiment of the invention in which hydrodesulfurization is carried out in two successive steps (e) and (f). Include.

Degradation of the sulfur-containing compound of the heavy fraction and / or intermediate fraction from step (d) (step (e)):

This step of applying to heavy gasoline (heavy fraction and / or intermediate fraction) obtained at the end of fractionation step (d) involves at least partially hydrocracking the sulfur-containing compound to form H ₂ S. The fraction of sulfur-containing compounds so converted is a function of the desired desulfurization rate.

This step is for example heavy gasoline in the presence of hydrogen under a temperature of about 210 ° C. to about 350 ° C., preferably 220 ° C. to 320 ° C. and generally at a pressure of about 1 to about 4 MPa, preferably 1.5 to 3 MPa. Can be carried out at least partially in sulfide form over a catalyst comprising at least one group VIB element and / or at least one group VIII element. The volumetric flow rate of the liquid is about 0.5 to about 20 h ⁻¹ (expressed as the volume of liquid per hour per catalyst volume), preferably 0.5 to 10 h ⁻¹ , very preferably 1 to 8 h ⁻¹ . The H ₂ / HC ratio is between 100 and 600 liters per liter, preferably between 200 and 500 liters per liter.

In order to at least partially hydrocrack the unsaturated sulfur-containing compound of gasoline according to the process of the invention, one or more Group VIII elements (groups 8, 9 and 10 metals of the new periodic table, namely iron, ruthenium, osmium, cobalt, One or more catalysts including rhodium, iridium, nickel, palladium or platinum) and / or one or more Group VIB metals (Group 6 metals of the new periodic table, ie chromium, molybdenum or tungsten) are used on suitable substrates.

The Group VIII metal content, expressed as oxides, is generally from 0.5 to 15% by weight, preferably from 1 to 10% by weight. The Group VIB metal content is generally 1.5 to 60% by weight, preferably 3 to 50% by weight. If a group VIII element is present it is preferably cobalt, and if a group VIB element is present it is usually molybdenum or tungsten. Combinations such as cobalt-molybdenum are preferred. Generally the substrate of the catalyst is a porous solid, for example alumina, silica-alumina or other porous solid, for example magnesia, silica or titanium oxide, which may be used alone or in combination with alumina or silica-alumina. . In order to reduce the hydrogenation of olefins present in heavy gasoline, it is desirable and advantageous to use a catalyst with a molybdenum density expressed in weight percent of MoO ₃ per unit area of greater than 0.07, preferably greater than 0.10. The specific surface area of the catalyst according to the invention is less than 190 m ² / g, more preferably 180 m ² / g Less than, very preferably 150 m ² / g Is less than.

The catalyst is preferably used at least partially in its immersed form. The sulphating step can be carried out in any manner known to those skilled in the art, either in situ or in situ.

In the process of the invention, the conversion of the sulfur-containing compound is at least 50%, preferably at least 90%.

Step (e) is carried out under conditions such that at least a portion of the sulfur-unsaturated compound, for example thiophene-based compound, is converted to a saturated compound, for example thiopan (or thiacyclopentane) or mercaptan, or These unsaturated sulfur-containing compounds are carried out to at least partially hydrocrack to form H ₂ S.

In the process according to a preferred embodiment of the invention, the conversion of unsaturated sulfur-containing compounds is at least 15%, preferably at least 50%. In the same step, the hydrogenation rate of the olefin is preferably less than 50%, more preferably less than 40% and very preferably less than 35% in this step. The effluent from the first hydrocracking step can then be passed to step (f) to effect decomposition of the saturated anti-containing compound into H ₂ S without performing any separation of liquid and gas.

Degradation of the sulfur-containing compound contained in the product from step (e) (step (f)):

In this step, the saturated sulfur compound is converted in the presence of hydrogen on a suitable catalyst. In addition, decomposition of the unhydrogenated unsaturated compound during step (e) can occur simultaneously. The conversion is carried out without significant hydrogenation of the olefin, ie during this step the hydrogenation of the olefin is generally limited to 20% by volume relative to the olefin content of the starting gasoline, preferably to 10% by volume relative to the olefin content of the starting gasoline. do.

Catalysts suitable for this step of the process of the invention generally comprise at least one basic element selected from the group VIII element and the group VIB element, preferably selected from the group consisting of nickel, cobalt, iron, molybdenum, and tungsten. Catalyst, but is not limited thereto. These metals may be used alone or in combination; They are supported and preferably used in their sulphate form. The catalyst of step (f) possesses different properties and / or compositions than those used in step (e). The base metal content of the catalyst according to the invention is generally about 1 to about 60% by weight, preferably 5 to 30% by weight and very preferably 10 to 25% by weight. Preferably, the catalyst is generally molded and is preferably in the form of balls, pellets, extrudates, for example trilobes. The metal can be incorporated into the catalyst by deposition on a preformed substrate; It may also be mixed with the substrate prior to the molding step. The metal is generally introduced in the form of precursor salts, generally water soluble salts such as nitrate and heptamolybdate. The introduction method is not specific to the present invention. Any other introduction method known to those skilled in the art may be suitable. Catalysts containing at least one Group VIII metal, in particular nickel, are very advantageously used.

The substrate of the catalyst used in this step of the present invention is generally a porous solid selected from refractory oxides such as alumina, silica and silica-alumina, magnesia as well as thian oxide and zinc oxide, these latter oxides being used alone. You may use it, mixing with alumina or silica-alumina. The substrate is preferably transitional alumina or silica having a specific surface area of 25 to 350 m ² / g. Natural compounds, for example diatomaceous earth or kaolin, are suitable as substrates for the catalysts used in this step of the invention.

The catalyst is preferably used at least partially in its immersed form. This provides the advantage of as far as possible limiting the risk of hydrogenation of unsaturated or aromatic compounds such as olefins during the initiation process. The sulphation step can be carried out using any technique known to those skilled in the art, either in situ or in situ.

After bleaching, the sulfur content of the catalyst is generally from 0.5 to 25% by weight, preferably from 4 to 20% by weight and very preferably from 4 to 10% by weight. The purpose of the hydrodesulfurization carried out in this step is to convert saturated sulfur-containing compounds of gasoline into H ₂ S, in which at least one prehydrogenation of the unsaturated compounds of sulfur has already been carried out during step (e). Effluents that meet certain specifications can be obtained in terms of the content of sulfur-containing compounds. The gasoline thus obtained shows only small octane losses. The treatment aimed at decomposing the saturated sulfur-containing compound derived from step (e) of the process is from about 280 ° C. to about 400 ° C., preferably from about 290 ° C. to about 380 ° C., more preferably from 310 ° C. to Nickel, cobalt, in the presence of hydrogen at a temperature of 360 ° C., very preferably 320 ° C. to 350 ° C. and generally at a pressure of about 0.5 to about 5 MPa, preferably 1 to 3 MPa, more preferably 1.5 to 3 MPa, It is carried out using a catalyst comprising at least one nonmetal selected from the group consisting of iron, molybdenum, tungsten. The volumetric flow rate of the liquid is about 0.5 to about 10 h ⁻¹ (expressed as the volume of liquid per hour per catalyst volume), preferably 1 to 8 h ⁻¹ . The H ₂ / HC ratio is adjusted based on the desired desulfurization rate within the range of about 100 to about 600 liters per liter, preferably 100 to 300 liters per liter. All or part of the hydrogen can be obtained from the recycle of hydrogen not consumed in step (e) (unconverted hydrogen), or in steps (a), (b) or (c) as needed. Under certain conditions it is possible to decompose saturated compounds contained in the effluent from step (c) into H ₂ S by using a second catalyst in this step. This practice results in a high overall hydrodesulfurization level at the end of every step of the process according to the invention, while minimizing octane losses due to saturation of the olefins, since the conversion of the olefins in step (e) is generally Is limited to 20% by volume or less, preferably 10% by volume or less.

In certain embodiments, depending on the nature of the starting gasoline feedstock, the feedstock is at least partially removed prior to step (c) for alkylation of at least a portion of the sulfur-containing compound present in the product from step (b). Most of its basic nitro-containing compounds are removed. According to a preferred embodiment, the basic nitrogen-containing compound contained in the starting gasoline is at least partially removed prior to introduction into step (a) for hydrogenation of the polyunsaturated compound. As a rule, the removal of the basic nitrogen-containing compound is carried out by a (wash) treatment with an aqueous acid solution. Thus, if the starting gasoline contains a basic nitrogen-containing compound, the basic nitrogen-containing compound is added prior to step (c) for alkylating at least a portion of the sulfur-containing compound present in the product derived from step (b). It is at least partially removed by treatment with an aqueous acid solution to be carried out. The washing is generally carried out before or after the selective hydrogenation of the polyunsaturated compound contained in the starting material in step (a).

The catalyst used in steps (a) and (f) is generally a separate sulfurized catalyst.

Example 1 (comparative)

The cracked gasoline was subjected to hydrogenation of diolefins under conditions in which saturated sulfur-containing light compounds present in the feedstock were partially converted to heavier compounds.

This treatment was carried out in a reactor operating continuously. The catalyst used was a nickel and molybdenum based catalyst (catalyst commercially available from Procatalyst Company under HR945). The reaction was carried out using a volumetric flow rate of 6 h ⁻¹ at 180 ° C. under a total pressure of 2.6 MPa. The H ₂ / feedstock ratio was 10 (liters of hydrogen per liter of feedstock).

The characteristics of the effluent after the hydrogenation of catalytic cracked gasoline and thiolefins and the conversion of light compounds are shown in Table 1 below.

Departure gasoline Gasoline After Hydrogenation (Steps (a) and (b)) Density 15/4 0.7215 0.7237 Bromine Number (gBr / 100 g) 78 74 Olefin (GC) weight% 43 40.5 MAV (mg / g) 10 0.2 Research octane 93 92.5 Motor octane 79.6 79.4 Mercaptan (ppm) 26 4 Total S (ppm) 350 350 Fractional Point (DS) 0.5% 2 2 5% 23 24 10% 30 31 50% 86 87 90% 141 143 95% 152 151 99.5% 175 175

At the end of the treatment, the gasoline was separated into two fractions: the light fraction and the heavy fraction whose fraction point represented 65% by weight of distilled gasoline corresponding to a temperature of 100 ° C. Separation was carried out on a batch distillation column consisting of 30 theoretical plates. The properties of the two fractions obtained are shown in Table 2 below.

Hard fraction Heavy fraction PI-100 100-175 Density 15/4 0.6826 0.7712 Bromine Number (gBr / 100 g) 91 48 MAV (mg / g) <0.2 <0.2 Research octane 93.4 91.8 Motor octane 79.9 79 Mercaptan (ppm) 3 4 Total S (ppm) 62 885 Fractional Point (DS) 0.5% 4 93 5% 20 99 10% 22 108 50% 60 128 90% 96 145 95% 99 152 99.5% 110 177

The light fractions exhibited olefin content, mercaptan content and sulfur content to the extent that they can be used directly, with specifications for the sulfur content of more than 60 ppm.

Heavy gasoline must be desulfurized before use. In all cases, this method made it impossible to produce desulfurized gasoline containing less than 40 ppm sulfur by combining light gasoline and heavy gasoline.

Example 2 (Comparative)

The catalytic cracked gasoline obtained in Example 1 after the hydrotreatment was separated into two fractions, the light fraction and the heavy fraction whose fraction points represent 20% by weight of distilled gasoline corresponding to a temperature of 55 ° C. Separation was performed on the same column as used in Example 1. The properties of the two fractions obtained are shown in Table 3 below.

Light gasoline Heavy gasoline PI-55 55-175 Density 15/4 0.65 0.77 Bromine Number (gBr / 100 g) 130 65 Olefin (GC) weight% 60 36 MAV (mg / g) <0.2 <0.2 Research octane 95 90.5 Motor octane 81.5 80 Mercaptan (ppm) <1 4 Total S (ppm) 2 437 Fractional Point (DS) 0.5% 4 52 5% 20 54 10% 22 67 50% 36 102 90% 41 138 95% 54 151 99.5% 72 176

The light gasoline produced by distillation exhibits mercaptan, diolefin and sulfur contents that can be used directly.

Heavy gasoline requires additional desulfurization.

Thus, heavy gasoline is hydrodesulfurized on some form of catalyst in an isothermal tubular reactor.

The first catalyst (catalyst A) is a transition introduced in the form of a ball having a specific surface area of 130 m ² / g and a pore volume of 0.9 ml / g by an aqueous solution containing molybdenum and cobalt in the form of ammonium heptamolybdate and cobalt nitrate Obtained by impregnation "without excess solution" of alumina. The catalyst was then dried and calcined in air at 500 ° C. The content of cobalt and molybdenum in the sample was 3% CoO and 14% MoO ₃ .

The second catalyst (catalyst B) was prepared from 140 m ² / g of transition alumina introduced in the form of a ball 2 mm in diameter. The pore volume was 1 ml per g of substrate. 1 kg of substrate was impregnated with 1 l of nickel nitrate solution. The catalyst was then dried at 120 ° C. and calcined for 1 hour under an air stream of 400 ° C. The nickel content of the catalyst was 20% by weight. 100 ml of catalyst A and 200 ml of catalyst B were placed in two reactors connected in series and the feedstock to be treated (heavy fraction) was first encountered with catalyst A and then with catalyst B. A zone for sampling the effluent from step (e) is provided between catalyst A and catalyst B. The catalysts were first immersed by treatment for 4 hours at a pressure of 3.4 MPa at 350 ° C. in contact with a feedstock containing 2% by weight of sulfur in dimethyl disulfide form in n-heptane.

The operating conditions of hydrodesulfurization are as follows: VVH = 1.33 h ^-1 , H ₂ / HC = 300 l / l, P = 2.0 MPa for the complete catalyst bed. The temperature of the catalyst zone containing catalyst A was 280 ° C, and the temperature of the catalyst zone containing catalyst B was 330 ° C.

The effluent thus obtained is shown in Table 4 below.

Starting heavy fraction Desulfurization heavy fraction Mixture of light gasoline and desulfurized heavy gasoline 55-175 55-175 PI-175 Density 15/4 0.7732 0.7696 0.7228 Bromine Number (gBr / 100 g) 65 38.5 56.2 Olefin (GC) weight% 36 25 32 MAV (mg / g) <0.2 <0.2 <0.2 Research octane 90.5 85.4 88.9 Motor octane 80 76 78.2 Mercaptan (ppm) 4 12 10.4 Total S (ppm) 437 30 25 Fractional Point (DS) 0.5% 52 2 5% 54 23 10% 67 30 50% 102 86 90% 138 141 95% 151 152 99.5% 176 175

This method described in patent application EP 1 077 247 can produce desulfurized gasoline whose content of mercaptans and diolefins is compatible with the grade required for gasoline.

In the special case of this example, the desulfurization rate was 92.8%, the residual sulfur content was 25 ppm, and the octane loss calculated as (RON + MON) / 2 was 2.75 points.

Example 3 (method according to the invention)

The catalytic cracked gasoline obtained in Example 1 after the hydrotreating according to [steps (a) and (b) according to the invention) is transferred to a reactor to increase the weight of the sulfur-containing compound by alkylation with olefins ( Step (c)) according to the invention. This step was carried out in a tubular reactor containing a catalyst with a phosphoric acid substrate supported on silica containing 20% by weight of phosphoric acid (catalyst C) and the operating conditions of the reactor were as follows: VVH = 1 h ^-1 , Pressure = 2.0 MPa, temperature = 180 ° C. Prior to injection into the reactor, the feedstock was supplemented with 500 ppm level of isopropanol to insure continuous hydration of the catalyst in the reactor.

Thus, the resulting effluent was separated into two fractions using a distillation column as described in Example 1. Distillation fraction point was set to 100 ° C; The light fraction represented 50% by weight of starting gasoline.

The properties of gasoline produced during the alkylation step (c) and fractionation step (d) are shown in Table 5 below.

Gasoline after weight gain by alkylation (step (c)) Light fraction (step (d)) Heavy fraction (step (d)) PI-240 PI-100 100-240 Density 15/4 0.7641 0.6921 0.8124 Bromine Number (gBr / 100 g) 62 53 72 MAV (mg / g) <0.2 <0.2 <0.2 Research octane 91.4 86.2 93.6 Motor octane 80.7 79.5 81.7 Mercaptan (ppm) 5 4 Total S (ppm) 350 18 670 Fractional Point (DS) 0.5% 6 6 94 5% 23 19 102 10% 30 24 108 50% 105 61 154 90% 206 97 210 95% 215 100 219 99.5% 240 111 238

The overall content of diolefins, mercaptans and sulfur in light gasoline recovered at the fractionation stage outlet was such that it could be used without further treatment. Heavy gasoline requires a desulfurization step.

Desulfurization of heavy gasoline (steps (e) and (f) of the process according to the invention) was carried out using the apparatus described in Example 2. The operating conditions were as follows: VVH = 1.33 h ^-1 , H ₂ / HC = 300 l / l, P = 2.0 MPa for the complete catalyst bed. The temperature of the catalyst zone comprising catalyst A is 290 ° C; The temperature of the catalyst zone containing catalyst B is 340 ° C.

The sulfur content of the gasoline thus prepared is 26 ppm or less. This gasoline does not require further treatment. This gasoline is recombined with the light gasoline recovered in step (d).

The characteristics of desulfurized heavy gasoline and recombinant gasoline are shown in Table 6 below.

Departure gasoline Light gasoline (stage (d)) Desulfurized heavy gasoline (step (e)) Recombinant Light and Heavy Gasoline PI-175 PI-100 100-240 PI-240 Density 15/4 0.7215 0.6921 0.8134 0.7683 Bromine Water (gBr / 100 g) 80 53 37 45 Olefin (GC) weight% 44 MAV (mg / g) 12 <0.2 <0.2 <0.2 Research octane 93 86.2 90.4 88.8 Motor octane 79.8 79.5 80.2 79.7 Mercamtan (ppm) 20 4 12 9 Non mercaptan sulfur (ppm) 330 14 24 17 Total S (ppm) 350 18 36 26

This process carried out according to the invention allows the production of desulfurized gasoline with limited octane loss, the mercaptan and diolefin contents of which are compatible with the grade required for gasoline.

In a particular example of this embodiment, the desulfurization rate is 92.6%; The residual sulfur content is 26 ppm and the octane loss calculated by the formula (RON + MON) / 2 is 2.15 points.

Claims (19)

A process for producing low sulfur gasoline from a starting gasoline containing at least 150 ppm by weight of a sulfur-containing compound, the method comprising the following steps: Selective hydrogenation of the nonaromatic polyunsaturated compound present in the starting gasoline (a); Sulfur-containing products in the form of mercaptans having 1 to 6 carbon atoms in the molecule and in the form of sulfides initially present in the gasoline introduced in step (a); And at least one step (b) aimed at increasing the molecular weight of at least one light sulfur-containing product selected from the group consisting of sulfur-containing products contained in the product from step (a); At least one step (c) for alkylating at least a portion of the sulfur-containing compound in the form of a thiophene-based compound present in the product from step (b) aimed at obtaining a sulfur-containing compound having a higher molecular weight ; The gasoline from step (c) is divided into two or more fractions, i.e. the first fraction (light gasoline) and the first fraction which is substantially free of sulfur and contains the lightest olefins of the unconverted starting gasoline of step (c) At least one step (d) for fractionation into at least one other fraction that is heavier and richer in sulfur-containing compounds; And At least one step (e) for treating at least one heavier fraction derived from step (d) on a catalyst capable of at least partially decomposing a sulfur-containing compound. The process of claim 1, wherein step (e) for treating one or more heavier fractions separated in step (d) on a catalyst capable of at least partially degrading a sulfur-containing compound limits hydrogenation of olefins on said catalyst. Carried out under conditions which may occur. 3. The H ₂ formed according to claim 1, wherein the H ₂ formed during step (e) on a catalyst and under conditions capable of at least partially decomposing the sulfur-containing compound not converted in step (e) with limited hydrogenation of the olefin. At least one step (f) for treating the product obtained in step (e) without removing S. The process of claim 1 or 2, wherein the starting gasoline is catalytically cracked gasoline with a final boiling point of 120 ° C to 230 ° C. The process of claim 3, wherein the conditions of step (f) decompose an unsaturated sulfur-containing compound and a linear, cyclic, or linear and cyclic saturated sulfur-containing compound that is not converted during step (e) with limited hydrogenation of the olefin. Selected to. The process according to claim 1 or 2 aimed at increasing the molecular weight of the light sulfur-containing product initially present in the gasoline introduced in step (a) and step (a) for hydrogenating the unsaturated compound ( b) is carried out simultaneously in a single reaction zone containing one or more beds of single catalyst. 3. The basic of claim 1, wherein the starting gasoline is at least partially removed prior to step (c) for alkylating at least a portion of the sulfur-containing compound present in the product derived from step (b). A nitrogen-containing compound. 8. The process of claim 7, wherein the basic nitrogen-containing compound contained in the starting gasoline is at least partially removed prior to introduction into step (a) for hydrogenation of the polyunsaturated compound. The method of claim 6, wherein the removal of the basic nitrogen-containing compound is carried out by treatment with an aqueous acid solution. 4. The method of claim 3, wherein the desulfurized heavy gasoline from step (f) is stripped using a cover gas. The process of claim 3, wherein step (e) and step (f) are carried out in at least two consecutive and separate reaction zones. 4. The process of claim 3 wherein at least a portion of the light gasoline from step (d) and the heavy gasoline from step (f) are mixed to form a total desulfurized gasoline. The process of claim 1 or 2, wherein the catalyst of step (e) comprises at least one group VIII element and at least one group VIB element. The process of claim 3 wherein the catalyst of step (f) comprises at least one Group VIII element. The process of claim 3, wherein the catalyst used in steps (e) and (f) is a separate sulphate catalyst. 4. The process of claim 3, wherein step (e) and step (f) are performed in two reactors arranged in series such that the second reactor as a whole treats the effluent of the first reactor. 3. The alkylation step (c) according to claim 1 or 2, wherein the alkylation step (c) converts a portion of the olefins in the starting gasoline into long branched olefins by the addition reaction between the olefins, and the weight of the portion of the aromatic compound is alkylated with the olefins. Performing under the conditions increased by. The process according to claim 1 or 2, wherein the heavy fraction from step (d) is transferred to a fractionation zone to obtain a sulfur rich heavy fraction and a lighter fraction of low sulfur. The process according to claim 1 or 2, wherein the gasoline derived from the hydrodesulfurization step (e) or (f) is transferred to a fractionation zone where a heavy fraction rich in sulfur and a lighter fraction of low sulfur can be obtained.