JP4385178B2 - Process for producing desulfurized gasoline from gasoline fractions containing converted gasoline - 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

  The present invention desulfurizes conversion gasoline, in particular gasoline obtained from catalytic cracking, fluidized bed catalytic cracking (FCC), coking (English) method, visbreaking (English) method, thermal cracking method, etc. It relates to the method of In this method, straight run gasoline (straight run in English) in which at least one of the above gasolines is mixed can also be processed. By using the method of the present invention, it is possible to achieve a high desulfurization rate while suppressing a decrease in octane number caused by olefin saturation as observed during the hydrodesulfurization reaction. The present invention relates to a process for producing gasoline having a low sulfur content, which includes hydrogenation, a step for converting a sulfur-containing compound, alkylating a sulfur-containing compound not converted in the preceding step. A process for the conversion, a light fraction and at least one heavy fraction and optionally a fractionation into one or more middle fractions, and hydrogenation of the heavy fraction and / or middle fraction Desulfurization. With this method, the total sulfur content of gasoline fractions, possibly containing C2, C3 or C4 hydrocarbons, is reduced to a very low level that is compatible with current and future regulations. The quality of the fraction can be improved. Further, even if this desulfurization is carried out, the yield of gasoline is not significantly reduced, and the decrease in octane number is minimized.

  When trying to produce reformate gasoline that meets the new environmental standards, it is particularly necessary to significantly reduce their sulfur concentration while minimizing the decrease in olefin concentration. Converted gasoline, and more specifically gasoline obtained from catalytic cracking, represents 30-50% of the gasoline pool, but its olefin content and sulfur content are high. Nearly 90% of the sulfur present in the reformed gasoline is attributed to catalytic cracking gasoline (FCC, “Fluid Catalytic Cracking” or fluidized bed catalytic cracking). Therefore, desulfurization (hydrodesulfurization) of gasoline and mainly FCC gasoline is extremely important for achieving the regulation value.

  Hydrodesulfurization of the feedstock sent to catalytic cracking typically yields gasoline containing 100 ppm sulfur. However, the hydroprocessing unit for catalytically cracking the feed material is operated under severe temperature and pressure conditions, so it consumes a large amount of hydrogen and the equipment cost is high. In addition, since all of the feedstock must be desulfurized, it is necessary to process a very large amount of feedstock.

  If carried out under standard conditions known to those skilled in the art, it is possible to reduce the sulfur content of the fraction by hydrodesulfurization of cracked gasoline. However, this method has great difficulties, and all olefins are saturated during the hydrotreatment, resulting in a very marked decrease in the octane number of the fraction.

  The teachings in the prior art are extremely non-specific, both in terms of sulfur content and in terms of aromatics content and preferred octane number values, to the standards currently in effect and future standards expected in 2005-2010. Numerous solutions have been devised to obtain suitable desulfurized gasoline. Thus, for example, it is possible to cite the method described in US Pat. No. 6,057,096, in which gasoline is fractionated into several, preferably three, fractions based on their respective boiling points, And it is taught that it is advantageous to desulfurize them in the presence of a catalyst comprising at least one metal of Group VIB and / or Group VIII, although the conditions may be different for each. The patent shows that the greatest effect is obtained when gasoline is fractionated into three fractions and a fraction having an intermediate boiling point is treated under mild conditions.

  It is also possible to cite the teachings of US Pat. No. 6,057,032 which describes a process for hydrodesulfurizing cracked gasoline, where the gasoline is first desulfurized with a first fraction rich in compounds that are easily desulfurized. It is separated into several fractions, including at least a second fraction rich in difficult compounds. Prior to this separation, an analysis must be performed to quantify the distribution of sulfur-containing compounds in advance. These analyzes are necessary to select equipment and separation conditions.

  Therefore, this application shows that the olefin content and octane number of the light cracked gasoline fraction are significantly reduced when the fraction is desulfurized without fractional distillation. In contrast, fractionating the light fractions into 7-20 fractions and analyzing the sulfur and olefin content of those fractions reveals the fraction or fractions with the highest sulfur-containing compounds. Then, they can be desulfurized simultaneously or separately and then mixed with other fractions (desulfurized or non-desulfurized). Such a procedure is complex and must be established each time the composition of the gasoline to be processed varies.

  The gasoline is fractionated and then introduced into different levels of hydrodesulfurization reactors, and the desulfurized fraction is converted over ZSM-5 zeolite to compensate for the octane reduction (isomerism). A method for hydrotreating gasoline has also been proposed (for example, see Patent Document 3). This isomerization involves cracking gasoline into lighter compounds.

  In these processes, the starting point of the gasoline to be treated is generally higher than 70 ° C., and again, light gasoline (compounds having a boiling point between C5 hydrocarbons of 5 carbon atoms up to 70 ° C.). For example, by softening.

  According to the teachings of US Pat. No. 6,057,049, this process for desulphurization of naphtha fractions containing olefinic gasoline includes a step of increasing the weight of the sulfur-containing compound by alkylation followed by two runs of the gasoline. The light gasoline thus obtained has almost no sulfur content.

  According to the teachings of US Pat. No. 6,057,059, this method for producing desulfurized gasoline includes separating gasoline into light and heavy gasoline. The light gasoline is sent to the reactor to increase the weight of the sulfur-containing compound by alkylation. The heavy gasoline is supplemented with reactive olefins and then sent to the reactor to increase the weight of the sulfur-containing compound by alkylation. Next, when the heavy gasoline and the light gasoline are mixed and then sent and subjected to distillation, it is possible to recover gasoline having almost no sulfur from the top of the column.

According to the teaching of US Pat. No. 6,057,056 by the present applicant, the gasoline to be desulfurized is treated in a process comprising the following steps, i.e. step a1) is a step for selective hydrogenation of diolefinic compounds, Any at least one step a2) is a step intended to increase the molecular weight of the light sulfur-containing product present in the starting gasoline to be desulfurized, and at least one step b) is a step a1) and / or a2 The gasoline obtained at the outlet is separated into two separate fractions, a light fraction that is substantially free of sulfur and contains the lightest olefins in the starting gasoline, and sulfur present in the starting gasoline. At least one process for separating the containing compound and / or another heavy fraction containing almost all of the sulfur-containing compound generated in step a2) c) by treating the heavy fraction, the unsaturated sulfur-containing compounds present in this fraction, in particular cyclic and even aromatic sulfur-containing compounds, in the olefins present in this fraction; Is a step that allows cracking or hydrogenation under conditions that inhibit hydrogenation of, and at least one step d) is a step by treating the gasoline generated from step c) Unsaturated sulfur-containing compounds not converted in c) and linear and / or cyclic saturated sulfur-containing compounds present in this gasoline generated in step c), which suppresses the hydrogenation of olefins present This is a process that makes it possible to decompose. In order to carry out this method, it is necessary to restrict the top temperature of the fractionation tower in order to obtain a top fraction which is substantially free of sulfur, in particular no thiophene. . If this is the case, this limitation is usually detrimental to the use of the entire process because the suppression of the temperature of the fraction recovered from the top of the fractionation tower results in a limit on the amount, This is because the amount of heavy fraction increases and the increased amount must be treated again in terms of reducing the sulfur content.
U.S. Pat. No. 4,131,537 European Patent Application Publication No. A 0 725 126 U.S. Pat. No. 5,290,427 US Pat. No. 5,599,441 US Pat. No. 6,024,865 European Patent A No. 1 077 247

  The present invention makes it possible to produce desulfurized gasoline while suppressing a decrease in octane number due to desulfurization. The system of the present invention is clearly different from the standard desulfurization system based on desulfurizing the entire gasoline. In some cases, these schemes use at least two distillates of gasoline, one distillate containing light gasoline and a heavy distillate, ie, a gasoline having a final boiling point higher than that of light gasoline. Separate into minutes.

  This heavy gasoline is desulfurized, for example, by treating or adsorbing sulfur-containing compounds with hydrogen. In systems involving hydrogen treatment, olefins undergo significant saturation, resulting in a significant decrease in octane number.

  This light gasoline can be desulfurized under mild conditions, including hydrodesulfurization, washing with basic solution or adsorption to solids, or softening by oxidation methods such as Universal Oil There is a Melox (registered trademark) method (extraction method is also possible) of the product (Universal Oil Product, UOP).

  In some systems, only heavy gasoline is required to be desulfurized, and sulfur-containing compounds (mercaptans) that are usually present in light gasoline are used for their weight in distillation or fractionation zones (in English). Increase in advance upstream from the splitter.

  As far as the process for increasing the weight of sulfur-containing compounds by alkylation presented here, it is possible to produce desulfurized light gasoline, while heavy sulfur-containing compounds and alkyls in heavy gasoline. The sulfur-containing compound whose weight has been increased by the conversion is concentrated. Therefore, in these methods, it is not possible to desulfurize the entire converted gasoline fraction, in particular the gasoline fraction obtained from the catalytic cracking unit. Furthermore, acid catalysis is utilized in methods of increasing the weight of sulfur-containing compounds by alkylation. The presence of diolefins and basic compounds (mainly nitrogen-containing compounds) in the gasoline to be treated may limit the service life of the catalyst.

The present invention relates to a process for producing gasoline with a low sulfur content, by which a gasoline fraction containing sulfur, preferably catalytic cracking or coking (term in English), or pyrolysis, or visbreaking ( It is possible to improve the quality of the whole gasoline fraction by mixing the gasoline fraction from (English terminology) in some cases with directly distilled gasoline, and while suppressing the sulfur content in the gasoline fraction to a very low level, There is no significant reduction in gasoline yield, and a decrease in octane number due to olefin hydrogenation can be minimized. The feedstock of the process according to the invention can optionally further comprise a gasoline fraction, where the C4 ^- fraction comprises hydrocarbons having 2, 3 or 4 carbon atoms.

The present invention relates to a process for producing low sulfur content gasoline from a starting gasoline comprising at least 150 ppm by weight, often at least 200 ppm and most often at least 300 ppm sulfur-containing compounds, comprising at least the following steps:
The step a) for selectively hydrogenating non-aromatic, polyunsaturated compounds present in the starting gasoline;
A step aimed at increasing the molecular weight of the light sulfur-containing product of at least one step b), the light sulfur-containing product being mainly present from the beginning in the gasoline introduced into step a) In addition, mercaptans having 1 to 6 carbon atoms in the molecule and sulfides often having 2 to 6 carbon atoms in the molecule, and / or those contained in the product generated in step a). Yes,
A step for alkylating at least one part of the sulfur-containing compound of at least one step c), wherein the sulfur-containing compound is mainly from step b) aimed at obtaining a higher molecular weight sulfur-containing compound; It takes the form of a thiophene compound present in the generated product,
A step of at least one step d) for distilling the gasoline generated from step c) into at least two fractions, the first fraction being substantially free of sulfur, The starting gasoline contains the lightest olefins (light gasoline) and at least one other fraction is a fraction that is heavier than the first fraction and contains more sulfur-containing compounds; Preferably at least one so-called heavy fraction comprises the majority of the sulfur-containing compounds present in the gasoline generated from step c) (heavy gasoline), and at least one step e) Treating at least one of the heavier fractions generated from step d) on a catalyst which makes it possible to at least partially decompose the sulfur-containing compounds. During this step e) it is preferred to treat the so-called heavy fraction separated in step d).

  The term “primarily” in steps b) and c) means that during that step of interest, at least 50% of the sulfur-containing compounds present in the form of compounds of the type specified therein are converted. Means.

  Step e) is often a step of treating on the catalyst at least one of the heaviest fractions separated in step d), thereby inhibiting olefin hydrogenation on the catalyst. Carried out under such conditions, the sulfur-containing compound can be at least partially decomposed.

In a preferred embodiment of the invention, two steps are carried out to treat the heavier fraction generated from step d) and preferably at least one of heavy gasoline:
A step for treating at least one of the heavier fractions separated in step d) of at least one step e) and preferably at least one of the heavy gasoline, whereby on the catalyst Enabling the sulfur-containing compound to be at least partially decomposed under conditions that inhibit olefin hydrogenation; and
A step for treating the product obtained in step e) of at least one step f) on the catalyst without removing the H ₂ S formed during this step e), thus The conditions include allowing the sulfur-containing compound that was not converted during step e) to be at least partially decomposed while inhibiting olefin hydrogenation, and preferably inhibiting olefin hydrogenation. However, it is carried out under conditions that make it possible to decompose unsaturated sulfur-containing compounds and linear and / or cyclic saturated sulfur-containing compounds that were not converted during step e).

  In the context of the present specification, the term polyunsaturated compound includes a diolefinic hydrocarbon-containing compound, ie two double bonds, in which the hydrocarbon-containing compound is more than two Included are diolefinic hydrocarbon-containing compounds that have heavy bonds but are not aromatic and hydrocarbon-containing compounds that are present in the starting gasoline with at least one triple bond. In most cases, the starting gasoline substantially contains diolefinic compounds as polyunsaturated compounds. In the sense herein, the low sulfur content gasoline obtained is a gasoline containing less than 150 ppm by weight, often less than 100 ppm and most often less than 80 ppm by weight.

  Step b) for converting light sulfur-containing compounds usually involves substantially the conversion of saturated sulfur-containing compounds having a boiling point of less than 120 ° C. This step can optionally be carried out on all or part of the starting gasoline at the same time as step a), in which case it is carried out in the same reactor or in different reactors. There may be. It can also be carried out individually on all or part of the hydrogenated gasoline in step a). In this step b), thiophene and thiophene compounds are hardly converted. Therefore, steps a) for hydrogenating this unsaturated compound and steps aimed at increasing the molecular weight of the saturated light sulfur-containing product that was originally present in the gasoline introduced into step a) b) can optionally be carried out simultaneously in a single reaction zone comprising one or more catalyst beds of a single catalyst.

  Step c) is a step for alkylating the sulfur-containing compound, and this sulfur-containing compound usually belongs to the group comprising thiophene, thiophene compounds and mercaptans present in the product generated from step b). . The mercaptan optionally present here was that formed in step a) and / or b) or was present in the starting gasoline but was not converted in steps a) and / or b). One of things. This step can be carried out in one or a plurality of reactors connected in series or in parallel. In the case of an apparatus with several reactors connected in series, the first reactor may serve as a guard bed for trapping basic compounds that may be present in the starting gasoline. These basic compounds can also be at least partially removed prior to the introduction of gasoline in step a) for hydrogenating polyunsaturated compounds. This removal is preferably carried out by treatment with an acidic aqueous solution. The operating conditions can be adjusted so that some of the starting gasoline olefins are converted to branched long chain olefins by addition reaction between the olefins. It is also possible to increase the weight of a part of the aromatic compound by alkylation with olefin by adjusting the operating conditions.

  Step d) for fractionating the gasoline finally obtained in step c) involves fractionating into at least two fractions, which are preferably substantially free of sulfur, Formed between the light fraction (light gasoline or light fraction) containing the lightest olefin of the starting gasoline and existing in the starting gasoline and / or steps a), b) and c). Most of the sulfur-containing compound is preferably a heavy fraction (gasoline or heavy fraction) concentrated therein. The gasoline obtained in step c) can also be separated into three or more fractions, for example a light fraction, at least one middle fraction, and a heavy fraction. In this case, the single or multiple middle distillates can also be sent to the catalytic reforming unit, usually after a strong desulfurization process.

  Step e) for treating heavy gasoline and / or middle distillate, which contains a proportion of sulfur-containing compounds that are considerably larger than those contained in the light distillate, treats this distillate on the catalyst. In the process, thereby conditioning the olefin hydrogenation on the catalyst, sulfur-containing compounds, especially cyclic sulfur-containing compounds and even even aromatic compounds such as thiophene compounds, for example. It becomes possible to at least partially decompose.

Step f) is a process for treating the product obtained in step e) without removing the H ₂ S formed during that step e). The sulfur-containing compound that was not converted during step e) is at least partially decomposed or hydrogenated and preferably unsaturated sulfur-containing compound that was not converted in step e) and linear And / or selected to allow cyclic saturated sulfur-containing compounds, particularly thiophene compounds and mercaptans, to be decomposed or hydrogenated.

  Steps e) and f) are most often carried out in at least two consecutive, separate reaction zones. The catalyst treatment carried out during steps e) and f) can be carried out in a single reactor comprising two catalysts or can be carried out in at least two separate reactors. If the process is carried out using two reactors, the latter two are connected in series, whereby the effluent at the outlet of the first reactor as a whole, preferably the first and the second. It is preferable to treat in the second reactor without separating the liquid and gas between the two reactors. It is also possible to carry out one and / or other steps e) and / or f) using a plurality of reactors in parallel or in series.

Furthermore, it is not necessary to remove the H ₂ S formed during step e) before sending the effluent from step e) to the inlet of the single or multiple hydrogenation reactors of step f).

Thus, one advantage of the method according to the invention is that it is not necessary to adjust the H ₂ S content between step e) and step f).

  Furthermore, it is preferable to carry out step g) after step f), but this step mixes the light gasoline separated in step d) with at least a portion of the heavy gasoline generated from step f). And forming a desulfurized gasoline as a whole for the purpose.

Preferably, all the desulfurized heavy gasoline generated from step f) is mixed with the light gasoline generated from step d) without separating the liquid and gas contained in the desulfurized heavy gasoline, In some cases, it is also possible to carry out the removal of H ₂ S in heavy gasoline, which is simply stripped with at least one cover gas and subjected to strong desulfurization. The heavy desulfurized heavy gasoline usually has a residual sulfur-containing compound of less than 50% by weight and often less than 20% by weight, based on the content of sulfur-containing compounds in the heavy gasoline present in step d). It is included.

  In some special cases, the quality of light gasoline and desulfurized heavy gasoline may be improved separately. In that case, it is not necessary to carry out step g).

For gasoline whose final boiling point exceeds 130 ° C., two additional steps may be required:
A step intended to remove the necessary basic compound before step c) in an additional step to remove the basic compound that can be washed with an acidic aqueous solution;
A step for fractionating gasoline produced from step d) for fractional distillation or one of steps e) or f) for hydrodesulfurization, from the gasoline so produced, A process aimed at separating a heavy fraction with an initial point of 210 ° C., for example, and a lighter fraction with an end point of 210 ° C., for example.

If this fractionation is carried out on the gasoline generated from step d), the lighter fraction is sent to step e).

  The feedstock of the process according to the invention is a gasoline fraction containing sulfur, a cracking unit (equipment), most often a gasoline fraction generated from a catalytic cracking unit, typically having a boiling range of 2 carbon atoms. Or from about the boiling point of 3 hydrocarbons (C2 or C3) to about 250 ° C, preferably from about the boiling point of 2 or 3 carbon atoms (C2 or C3) to about 220 ° C, more preferably carbon. From about the boiling point of a hydrocarbon of 5 atoms (C5) to about 220 ° C. More specifically, the process of the present invention is applied to catalytically cracked gasoline having a final boiling point of about 120 ° C to about 230 ° C.

The advantages of this method over the prior art are as follows:
1. The diene compound contained in the starting gasoline from the viewpoint of suppressing the decrease in the activity of the catalyst for alkylating the sulfur-containing compound in the subsequent step c) and at the same time suppressing the formation of rubber-like substances in the gasoline. And optionally removing the acetylene compound.

  2. Light mercaptans have been removed to produce softened light gasoline that does not require refining or desulfurization in later processes.

  3. Increase the production of desulfurized light gasoline recovered at the top of the fractionation tower, thereby reducing the amount of gasoline to be treated by hydrodesulfurization.

  4). Production of branched olefin rich heavy gasoline production by fractional distillation whose octane number is not significantly affected by olefin saturation.

  5). The selective desulfurization of heavy gasoline (or the result of lateral drawing-off) suppresses the saturation of olefins and the decrease in octane number of heavy gasoline.

  6). Compared to the starting gasoline, the vapor pressure of the produced gasoline is reduced overall.

In the present invention, desulfurization with reduced sulfur content by mixing gasoline, preferably from gasoline generated from a unit for catalytic cracking, coking, visbreaking or pyrolysis, optionally mixed with saturated gasoline. A method is described which makes it possible to obtain gasoline, in which the gasoline is first subjected to a selective hydrotreatment of diolefins and then mercaptans having 1 to 6 carbon atoms in the molecule and many In the form of sulfides having 2 to 6 carbon atoms, after the fractionation, the sulfur-containing compounds in the soot gasoline found in light gasoline are converted and after the fractionation step of the process according to the invention Process for making it present in a substantially heavy stream, converted sulfur-containing compounds in the form of mercaptans and sulfides Sulfur-containing compounds present in the form of thiophenic compounds in gasoline generated from because step there is a step for alkylation. In this process, it is also possible to adjust the operating conditions to promote the alkylation reaction of olefins to olefins and aromatics, and in particular to lower the vapor pressure of gasoline. At least one fraction generated from the fractionation step, preferably a heavy fraction or middle fraction, can also be treated in a step for converting those sulfur-containing compounds into H ₂ S (hydrogen sulfide). In this case, it is possible to prevent or suppress the saturation of the olefin.

  After said fractionation, heavy gasoline or at least one middle distillate is treated in the hydrodesulfurization section, preferably in the presence of a hydrodesulfurization catalyst or optionally an adsorbent. In the process according to the present invention, it is not necessary to desulfurize the light fraction because the majority of the sulfur-containing compounds initially present in the gasoline are heavy in the fractionation step d). This fractionation step is carried out after the step for hydrogenation and conversion of the sulfur-containing compound, since it is present in the mass fraction and optionally in one or more middle fractions. After step (step b), thiophene compounds and optionally mercaptans, in particular in steps a) and b), were not converted by alkylating at least part of the unconverted sulfur-containing compound in step b) It is after the step (step c) for converting the formed residual mercaptan (step c).

  This approach makes it possible to finally obtain a desulfurized gasoline that has a high desulfurization rate but does not have a significant decrease in olefin content or octane number; and to achieve this, light gasoline is hydrodesulfurized. There is no need to process by means of sections or softening sections and no need to rely on a method that allows the octane number of the gasoline to be restored. By this method, a high desulfurization rate can be achieved under reasonable operating conditions, which will be described later.

  Sulfur-containing radicals contained in the feedstock treated by the method of the present invention include mercaptans, sulfides, disulfides and / or heterocyclic compounds such as thiophene or alkylthiophenes, or heavier compounds such as benzothiophene and / or Or dibenzothiophene.

  It is preferred to limit the gasoline fractionation point to prevent the presence of sulfur-containing compounds in light gasoline. In the absence of a reactor for alkylating sulfur-containing compounds, only C5 olefins and small amounts of C6 olefins are separated in light gasoline so that large amounts of thiophene fractions are not mixed into this fraction. Is also possible. Thus, the process according to the present invention comprises a step for converting thiophene, more generally a thiophene-based compound, for example alkylation provided upstream of the fractionation section, as in the detailed embodiment described below. It is convenient to carry out at the same time as the section or integrated into the section.

  In order to recover most of the light gasoline and to suppress the sulfur content of this fraction without further treatment, the feedstock in step b) is most commonly in its molecule. Treating under conditions and catalysts that allow conversion of light sulfur-containing compounds present in the form of mercaptans and sulfides having 2 to 6 carbon atoms to sulfur-containing compounds with higher boiling points It can be said that it is preferable. Those high-boiling sulfur-containing compounds are optionally found in at least one middle distillate or heavy gasoline after separation. These middle and / or heavy fractions can then be desulfurized. In order to carry out this desulfurization, a hydrodesulfurization catalyst capable of suppressing olefin saturation under certain conditions is used, or according to a preferred embodiment of the present invention, a high desulfurization rate. The catalyst is of a type that makes it possible to suppress the hydrogenation rate of the olefin and consequently the decrease in octane number.

  The sulfur content of gasoline fractions produced by catalytic cracking and in particular fluidized bed catalytic cracking (FCC) is the sulfur content of feedstock treated with FCC, the presence or absence of pretreatment of the FCC feedstock, and the end of the fraction. It is affected by the remaining points. In general, the sulfur content of the overall gasoline fraction, in particular the gasoline fraction obtained with FCC, is greater than 150 ppm by weight and more often greater than 500 ppm by weight. In gasolines with end points above 200 ° C., their sulfur content often exceeds 1,000 ppm by weight, and in some cases even reaches values on the order of 4,000 to 5,000 ppm by weight. possible.

  The process according to the invention is used in particular when high desulfurization rates of gasoline are required, which means that the gasoline after desulfurization is at most 10% of the sulfur of the starting gasoline, in some cases at most 5%, Is the case when it contains at most 2% of the sulfur of the starting gasoline, which, in terms of desulfurization rate, corresponds to over 90%, or even over 95% or 98%.

The method according to the invention comprises at least the following steps a) to e):
Step a), a step for selectively hydrogenating diolefins: This step is aimed at a catalyst for increasing the weight of sulfur-containing compounds by alkylation during step c) described below. The removal of diolefins, which results in a decrease in activity in a short time and can produce rubbery substances in desulfurized gasoline. This step passes the effluent, preferably the effluent consisting of the entire gasoline fraction, over a catalyst that allows the selective hydrogenation of diolefins in gasoline without hydrogenating the olefins. To implement.

  Step b), Step for increasing the weight of mercaptans and light sulfides on supported metal-based catalysts: This reaction can be carried out in a reactor for the selective hydrogenation of diolefins. This step involves converting all or part of the starting gasoline or gasoline hydrogenated in step a), preferably all of the starting gasoline or gasoline hydrogenated in step a), into a light sulfur-containing compound (eg ethyl mercaptan, Propyl mercaptan) is allowed to react with all or part of the olefin and flow over a catalyst that can be converted to a heavier sulfur-containing compound. This step can be performed, for example, on one catalyst that can both hydrogenate diolefins and react light sulfur-containing compounds with preferably olefins to convert to heavier sulfur-containing compounds. Alternatively, it is carried out at the same time as step a) by flowing over another catalyst which makes it possible to carry out this conversion in the same reactor used to carry out step a).

  Step c) is a step for increasing the weight of the sulfur-containing compound by alkylation. This step makes it possible to remove most of the sulfur-containing compounds present in the form of thiophene compounds by a reaction of adding to olefins. This step consists of flowing all or part of the gasoline obtained in step b) over a catalyst having an acid function, which adds a sulfur-containing compound in the form of mercaptans and sulfides to the olefin. It is also possible to alkylate thiophene and thiophene derivatives with these same olefins.

  Step for fractionating the gasoline finally obtained in step d) and step c): This step is aimed at producing light desulfurized gasoline at the top of the distillation column. The gasoline recovered in this way is low in sulfur and in most cases does not need to be further processed. This light gasoline with low sulfur content is most often sent directly to the gasoline storage zone (according to the term most commonly used by those skilled in the art, a gasoline pool), preferably without additional post-treatment. . Gasoline recovered from the bottom of the column is enriched with sulfur-containing compounds that were originally present in the feedstock. The column can also be provided with a side draw so that, for example, one or more middle distillates can be obtained.

  In step e), gasoline at the bottom of the column and / or gasoline contained in the middle distillate generated from step d) is desulfurized by hydrotreatment.

  In a preferred embodiment of the present invention, the bottom gasoline generated from step d) and / or the gasoline contained in the middle distillate is used, and in step e), the olefin saturation is partially reduced to suppress a decrease in octane number. Desulfurize under the conditions and catalyst.

In a more preferred embodiment of the present invention, steps e) and f) are continued to suppress olefin saturation of the bottom gasoline generated from step d) and / or the gasoline contained in the middle distillate. It is desulfurized by hydrotreating by a method that makes it possible. In practice, the embodiment of selective hydrodesulfurization makes it possible to suppress olefin saturation and, as a result, to suppress a decrease in gasoline octane number. Heavy gasoline and / or at least one such desulfurized intermediate gasoline is then optionally stripped (i.e., preferably a gas stream comprising one or more cover gases is passed through the gasoline. And H ₂ S produced during this desulfurization is optionally removed.

As a variant of the process according to the invention, it is also possible to link at least one reaction section with a fractionation column. There, the single or multiple reaction sections act on at least one fraction taken inside the fractionation column and send the effluent of this reaction section to the fractionation column. The single or multiple reaction sections thus combined with the fractionation column of step d) can be selected from the group consisting of the reaction sections of the following steps:
Conversion of sulfur-containing compounds such as thiophene, thiophene-based compounds and optionally mercaptans by alkylation (step c)
Desulfurization of middle distillate and / or desulfurization of heavy fraction ((step e) and / or step f)).

  The application of such a device comprising a fractionation column in combination with an external reactor that can be used in the process according to the invention, for example in the field of petroleum refining and petrochemistry, is described in US Pat. No. 5,1777,283. No. 5,817,227 and US Pat. No. 5,888,355.

  In another variant of the process according to the invention, it is also possible to use a reaction column instead of a fractionation column, i.e. in this case at least one of said reaction sections is placed in the fractionation column (reaction section Present in the column), preferably in the zone where the concentration of the reactants reaches a maximum. Thus, for example, in the case of step c) for converting sulfur-containing compounds such as thiophene compounds by alkylation, it is preferable to provide the reaction section in a zone where the concentration of those compounds is maximized.

  In a preferred variant of the process according to the invention, the reaction section inside the column is selected from the group consisting of the following reaction sections: sulfur-containing compounds such as thiophene, thiophene-based compounds and possibly mercaptans are converted by alkylation. (Step c)), desulfurization of middle distillate and / or desulfurization of heavy distillate ((step e) and / or step f).

  In a very preferred embodiment of the process according to the invention, the reaction section is provided in the middle of the fractionation column and constitutes a compound with an intermediate boiling point, for example an intermediate fraction, at the end of the fractionation step alone or heavy fraction. In addition, the compound recovered from the bottom of the column is treated. The heavy fraction is then processed in an external reactor, which may or may not be associated with a fractionation column.

  Such reaction columns are known to those skilled in the art, for example, US Pat. No. 5,368,691, US Pat. No. 5,523,062, French Patent 2,737,131. , French Patent No. 2,737,132, European Patent Application Publication No. 0 461 855, and the like.

  Other variants of the process according to the invention include the use of both a reaction column comprising at least one reaction section and an external reactor (which may or may not be coupled to said column). included. Such a modification is described, for example, in International Publication No. 00/15319.

  The variants described above are merely illustrative of possible variations in the method according to the invention. In practice, the process according to the present invention is such that the reaction section (steps a), b), c), e) or f)) is linked to the fractionation column of step d) or placed inside said column. The effluent from the single or multiple reaction sections is not recycled to the fractionation column without being externally coupled to the column. .

  One of the advantages of the process according to the invention is that there is almost no need to desulfurize the light fraction of gasoline generated from the fractionation. By converting sulfur-containing compounds and / or thiophene compounds (steps b) and / or c)), in practice, the content of sulfur-containing compounds in the light fraction and possibly in at least one middle fraction is reduced. It is greatly reduced and, in general, the majority of these compounds can be recovered in the heavy fraction and possibly in one or more middle fractions.

  Steps b) and c) differ from each other in the following points. That is, in step b) the conversion of the thiophene compound is generally less than 60% by weight, more preferably less than 40% by weight, whereas in step c) the conversion of said compound is often greater than 80% by weight, preferably Is greater than 90% by weight, very preferably greater than 95% by weight. In fact, step b) substantially heavyens mercaptans and light sulfides, whereas step c) substantially heavyens thiophene compounds.

  Even with this operation, the majority of the olefin in the light fraction, and in some cases at least one middle fraction that does not require strong desulfurization, is maintained. The content of sulfur-containing compounds in the light fraction thus obtained is generally less than 100 ppm, preferably less than 50 ppm, more preferably less than 20 ppm and very particularly preferably less than 10 ppm.

  Another advantage is that the gasoline desulfurized using the process according to the invention has a particularly low content of residual sulfur-containing compounds and the gasoline octane number is maintained at a high level.

  Each step of the method according to the invention is described in more detail below.

-Hydrogenation of diolefin (step a):
Hydrogenation of dienes is a process that allows the removal of almost all dienes present in the gasoline fraction containing sulfur to be treated prior to hydrodesulfurization. This is the first step in the process according to the invention (step a), preferably in the presence of a catalyst comprising at least one Group VIII metal selected from the group consisting of platinum, palladium and nickel and a support. It is preferable to carry out. For example, nickel-based or palladium-based catalysts are used that are deposited on an inert support, such as alumina, silica, or a support containing at least 50% alumina.

The pressure used is suitably such that a portion of the gasoline to be treated, 60%, preferably more than 80%, more preferably more than 95% by weight, can be maintained in a liquid state in the reactor. Most commonly, it is about 0.4 to about 5 MPa, preferably greater than 1 MPa, more preferably 1 to 4 MPa. The volumetric flow rate ratio of the liquid to be treated per hour is about 1 to about 20 h ⁻¹ (feed feed volume per hour of 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., and is a temperature that can sufficiently convert the diolefin. Most preferably, the upper temperature limit is 180 ° C. The ratio of hydrogen to feedstock in liters is generally 1-50 liters / liter, preferably 2-30 liters, more preferably 3-25 liters / liter.

  The selection of operating conditions is particularly important. Most commonly, the operation is carried out under pressure in the presence of a slight excess of hydrogen over the stoichiometric amount required to hydrogenate the diolefin. Hydrogen and feedstock to be treated are injected in an upward or downward stream, preferably in a reactor equipped with a fixed catalyst bed.

  A bimetallic catalyst may be formed by combining the main metal with another metal such as molybdenum or tungsten. The use of such a catalyst is claimed in French patent 2 764 299.

  Catalytic cracked gasoline may contain up to several weight percent (%) of diolefin. After hydrogenation, the diolefin content is generally less than 3000 ppm, even less than 2500 ppm, more preferably less than 1500 ppm. In some cases, it may be less than 500 ppm. The diene content after selective hydrogenation can even be less than 250 ppm if necessary.

  In a specific embodiment of the process according to the invention, the step of hydrogenating the diene is carried out in a catalytic hydrogenation reactor, which is necessary to carry out the desired reaction with the entire feedstock. There is a catalytic reaction zone through which a significant amount of hydrogen passes.

-Conversion of light sulfur compounds (step b):
This step is accompanied by heavy gasoline with light sulfur compounds, ie the soot compounds found in light gasoline (after fractionation in step d) at the end of step a) for hydrogenating the diene. Conversion to a heavier sulfur-containing compound. This light sulfur-containing compound is preferably selected from the group of mercaptans having 1 to 6 carbon atoms and sulfides having 2 to 6 carbon atoms. This transformation is based on at least one member of group VIII (groups 8, 9 and 10 of the new periodic table) of the periodic table (Handbook of Chemistry and Physics, 45th edition, 1964-1965). It is preferably carried out on a catalyst containing elements. The catalyst is selected from those that particularly promote reactions that produce heavier sulfides or mercaptans from light mercaptans and olefins. Other compounds, for example can be converted optionally COS and CS ₂ as well.

  This step can optionally be performed simultaneously with step a). For example, it would be particularly advantageous if it could be operated under conditions that would convert at least some of the mercaptan form of the compound during the hydrogenation of the diolefin. In this way, the mercaptan content can be reduced to some extent. To do this, the hydrogenation process of the diene described in EP-A-0 832 958, which preferably uses a palladium-based catalyst, or French Patent No. 2,720,754. The methods described in the specification can be used.

  Another possibility is to use a nickel-based catalyst, which may be the same as or different from the catalyst of step a), for example in US Pat. No. 3,691,066. The catalyst recommended in the process allows the conversion of mercaptans (butyl mercaptans) into heavier sulfur-containing compounds (sulfides).

Another possibility for carrying out this step is to at least partially hydrogenate thiophene to thiophane with a boiling point higher than that of thiophene (boiling point 121 ° C.). This step can be carried out with a nickel, platinum or palladium based catalyst. In this case, the temperature is generally 100 to 300 ° C., preferably 150 to 250 ° C. The ratio of H ₂ / feed material is adjusted to 1 to 20 liters / liter, preferably 3 to 15 liters / liter to further promote the hydrogenation of the thiophene compound if possible, and the olefins present in the feed material Suppresses hydrogenation. The volume flow rate ratio 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 compounds by alkylation (step c):
This step preferably consists of flowing the entire fraction generated from step b) over a catalyst having an acid function, the catalyst comprising addition reaction of sulfur-containing compounds in the form of mercaptans to olefins, and the same It is possible to proceed the alkylation reaction of thiophene and thiophene derivatives with olefins. By adjusting the operating conditions, the desired conversion can be carried out such that the conversion of thiophene and / or thiophene compounds exceeds 80% by weight, preferably more than 90% by weight, very preferably more than 95% by weight. Like that. Other compounds, such as COS and CS ₂ is also optionally can be converted in.

  During this process, some of the olefins in the starting gasoline are converted to branched long chain olefins by addition reaction (oligomerization) between the olefins, and some of the aromatic compounds are alkylated by the olefins. The weight increases due to the conversion.

  For the purpose of suppressing the oligomerization activity of the optionally used acid catalyst, a compound known to suppress the oligomerization activity of the acid catalyst, such as alcohol, ether or water, may be added to gasoline.

  During the alkylation, a thiophene compound having a boiling point of about 60 ° C. to about 160 ° C. reacts with the olefin at a conversion of more than 80% by weight, preferably more than 90% by weight, more than the boiling point of the starting thiophene compound. Forms thiophene alkyl with a fairly high boiling point.

  Some or all of the benzene can also be removed by alkylation with olefins.

  A major feature of these compounds with increased molecular weight is that the boiling point is higher than that of the alkylated one. In this way, the theoretical boiling point (84 ° C.) of thiophene changes to 150 ° C. of thiophene alkyl. Combining this reaction with an olefin addition reaction usually results in an increase in the weight of the gasoline, particularly when the gasoline fraction and / or the starting gasoline is light, and the vapor pressure decreases.

  This alkylation step is carried out in the presence of an acid catalyst. As the catalyst, resins, zeolites, clays, various functionalized silicas or various silicoaluminates having acidity, or various grafted substrates having acidic functional groups can be used equally. The ratio of the feed material volume to be injected to the catalyst volume is 0.1 to 10 liter / liter / hour, preferably 0.5 to 4 liter / liter / hour. More particularly, this alkylation step is carried out in the presence of at least one acid catalyst selected from the group consisting of: a Bronsted acid (eg phosphoric acid, sulfuric acid, boric acid, fluorinated). Examples of the carrier include silica, alumina or alumina silica, silicoaluminate, titanosilicate, mixed alumina titanium compound, clay, resin, organic solvent soluble or water soluble. At least one oxide of at least one organometallic compound (selected from the group consisting of alkyl and / or alkoxy metals of at least one element such as titanium, zirconium, silicon, germanium, tin, tantalum, niobium, etc.) For example, alumina (gamma, delta, eta, single or mixed), silica, aluminum Minashirika is titanium silicalite, mixed oxides obtained by grafting various solids with a zirconium silica or various acidity such. In a specific embodiment of the invention, at least two of the above catalysts are used in a ratio of 95/5 to 5/95, preferably 85/15 to 15/85, and very preferably 70/30. To 30/70 can also be used as a physical mixture.

  The temperature in this step is usually from about 10 to about 350 ° C., but will vary depending on the type of catalyst and the strength of the acidity. Therefore, in the case of a supported phosphoric acid-based catalyst, the temperature is usually about 50 to about 250 ° C, preferably about 100 to about 210 ° C.

  The molar ratio of olefin to thiophene compound is greater than 10 mol / mol, preferably greater than 100 mol / mol.

  The operation pressure in this step is generally 0.1 to 3 MPa, but preferably the pressure is such that the feed material is in a liquid state under the temperature and pressure conditions, or a pressure higher than 0.5 MPa.

  At least a portion, preferably all, of the effluent generated from step c) for converting the sulfur-containing compound is sent to a fractionation unit (step d)), where at least two fractions, a light fraction and a heavy fraction The heavy fraction is preferably optionally mixed with the middle distillate before the whole is mixed in one stage (step e) or two stages of continuous desulfurization (step e) and step f)) To the desulfurization zone operating at

--- Separation of gasoline generated from step c) into at least two fractions (step d):
In a first variant of the process according to the invention, the gasoline is fractionated into two fractions:
Other treatments with a light fraction, limited, preferably less than about 100 ppm, very preferably less than about 20 ppm, and therefore usually aimed at reducing its sulfur content This fraction can be used even if it is not carried out.

  A heavy fraction in which most of the sulfur that was originally present in the feedstock is suitably concentrated.

  This separation can be preferably carried out by means of a standard distillation column (splitter in English). This fractionation tower must be separable into a light fraction of gasoline that contains only a small percentage of sulfur and a heavy fraction that contains most of the sulfur that was originally present in the starting gasoline. Don't be.

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

  The light gasoline obtained at the end of this separation usually contains hydrocarbon-containing fractions of 5, 6 and 7 carbon atoms. In general, the sulfur content of this light fraction is low, so if this light fraction is used as fuel, it is usually not necessary to pre-treat.

  In this case, it is preferable to fractionate gasoline into at least two fractions having the following properties.

  A so-called light fraction (fraction L) having a boiling point of preferably less than about 120 ° C. The temperature here is given as an example, and generally corresponds to the maximum temperature for making the sulfur content less than 20 ppm.

  -At least one so-called heavy fraction (fraction H1) whose boiling point exceeds about 100 ° C.

The light fraction L is preferably injected into a flask for gas-liquid separation to separate unconsumed hydrogen and H ₂ S produced during steps a) and / or b) and / or c). The olefin is then usually of 5 to 7 carbon atoms.

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

  In a second variant of the process according to the invention, the gasoline is fractionated into at least three fractions: a light fraction, a heavy fraction and at least one middle fraction.

  The light fraction is the same as described above. Middle distillate I2 has a boiling point, by way of example, of at least 100 ° C., at most about 140 ° C., and even about 160 ° C. This fraction can be treated in step e) of the process according to the invention and then optionally in step f). In addition, the heavy fraction H2 has a boiling point generally higher than about 160 ° C or about 140 ° C. In this case, the middle fraction plus heavy fraction unit is equivalent to the heavy fraction H1 when fractionation is limited to two fractions.

  Heavy fraction H2, whose boiling point is generally higher than about 160 ° C or about 140 ° C, is sent to the desulfurization zone.

  In another process of the process according to the invention, the product generated from step c) is fractionated to produce at least three fractions, namely a light fraction (L), at least one middle fraction exhibiting the above properties. It is also possible to divide into a fraction (I2) and at least one heavy fraction (H2).

  Middle distillate I2, whose boiling point is between about 100 ° C. and about 120 ° C. or about 160 ° C., is sent to a unit for converting sulfur-containing compounds according to step c) or recycled to this step c) can do.

  After step d), the fraction or fractions I2 can be fractionated again and fractionated into an intermediate fraction I3 and a heavy fraction H3. The fraction H3 obtained in this way can optionally be mixed with the fraction H2 preferably before desulfurization, and the fraction I3 is converted into a unit for converting the sulfur-containing compounds of step c). Can be sent or recycled to this step c).

  In the following description, the conditions for step e) include conditions for carrying out a single desulfurization step and the present invention when hydrodesulfurization is carried out in two successive steps e) and f). In the preferred embodiment.

-Decomposition of sulfur-containing compounds of heavy fraction and / or middle fraction generated from step d) (step e):
This step applied to the heavy gasoline (heavy fraction and / or middle distillate) finally obtained in fractionation step d) comprises at least partly hydrocracking the sulfur-containing compound to produce H _2. S is formed. The proportion of sulfur-containing compounds converted in this way is a function of the desired desulfurization rate.

This step can be performed, for example, by flowing heavy gasoline over the catalyst in the presence of hydrogen, the catalyst comprising at least one Group VIII element and / or at least partially sulfide. At least one Group VIB element in the form, having a temperature of about 210 ° C. to about 350 ° C., preferably 220 ° C. to 320 ° C., and a pressure of generally about 1 to about 4 MPa, preferably 1.5 to 3 MPa. . The liquid volume flow ratio in this case is about 0.5 to about 20 h ⁻¹ (expressed in volume of liquid per unit volume of catalyst per hour), preferably 0.5 to 10 h ⁻¹ , very preferably 1 ~ 8h- ¹ . H ₂ / HC ratio is from 100 to 600 liters / liter, preferably 200 to 500 liters / liter.

  In order to at least partially hydrocrack the unsaturated sulfur-containing compounds of gasoline according to the process of the invention, at least one catalyst is generally used on a suitable support, the catalyst comprising at least One group VIII element (metals of Groups 8, 9 and 10 of the new periodic table, ie iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium or platinum) and / or at least one Group VIB elements (group 6 metals of the new periodic table, ie chromium, molybdenum or tungsten) are included.

The content of Group VIII metal (expressed in oxide form) is generally from 0.5 to 15% by weight, preferably from 1 to 10% by weight. The content of the Group VIB metal is generally 1.5-60% by weight, preferably 3-50% by weight. If a Group VIII element is present, cobalt is preferred, and if a Group VIb element is present, it is usually molybdenum or tungsten. Combinations such as cobalt and molybdenum are preferred. The catalyst support is usually a porous solid, such as alumina, silica alumina, or other porous solids such as magnesia, silica or titanium oxide alone or in a mixture with alumina or silica alumina. In order to suppress the hydrogenation of olefins present in heavy gasoline, a catalyst whose molybdenum density (weight percent of MoO ₃ per unit surface area) is greater than 0.07, preferably greater than 0.10. It is advantageous to use The specific surface area of the catalyst of the present invention is preferably less than 190 m ² / g, more preferably less than 180 m ² / g, and even more preferably less than 150 m ² / g.

  The catalyst is preferably used at least partially in its sulfurized form. This sulfiding step may be performed using any technique known to those skilled in the art and may be in situ or ex situ.

  In the process according to the invention, the conversion of the sulfur-containing compound is higher than 50%, preferably higher than 90%.

Step e) involves the conversion of at least some of the unsaturated compounds of sulfur, such as thiophene compounds, to saturated compounds such as thiophane (or thiacyclopentane) or mercaptans, or else of these unsaturated sulfur-containing compounds The conditions are such that the formation of H ₂ S by at least partial hydrogenolysis is observed.

In the process according to this preferred embodiment of the invention, the conversion of unsaturated sulfur-containing compounds is greater than 15%, preferably greater than 50%. The hydrogenation rate of olefins during the process in the same step is preferably less than 50%, more preferably less than 40% and very preferably less than 35%. The effluent obtained from this first hydrocracking step is then subjected to step f) which makes it possible to crack the saturated sulfur-containing compound into H ₂ S, preferably without any liquid gas separation. send.

-Decomposition of sulfur-containing compounds contained in the product generated from step e) (step f):
In this step, the saturated sulfur compound is converted in the presence of hydrogen under a suitable catalyst. Decomposition of unsaturated compounds that were not hydrogenated during step e) can also occur simultaneously. This conversion is carried out without significant hydrogenation of the olefins, ie the olefin hydrogenation rate during this process is usually up to 20% by volume, preferably from the starting gasoline, based on the olefin content of the starting gasoline. Up to 10% by volume based on the olefin content.

  Suitable catalysts for this step of the process according to the invention are selected from the elements of group VIII and group VIB, preferably at least one selected from the group consisting of nickel, cobalt, iron, molybdenum and tungsten. However, the catalyst is not limited to these catalysts. These metals may be used alone or in combination, but are preferably supported and used in a sulfurized form. The catalyst in step f) preferably has different properties and / or compositions than the catalyst used in step e). The base metal content of the catalyst according to the invention is generally from about 1 to about 60% by weight, preferably from 5 to 30% by weight and very preferably from 10 to 25% by weight. Preferably, the catalyst is usually shaped and preferably in the form of spheres, pellets, extrudates, such as trilobes. The metal can be added to the catalyst by precipitating it on a preformed carrier, but it can also be mixed with the carrier in the step before molding. The metal is generally introduced in the form of a precursor salt such as nitrate or heptamolybdate which is usually water soluble. Such an introduction method is not unique to the present invention. Any method of introduction known to those skilled in the art may be used. Catalysts containing at least one Group VIII element, in particular nickel, can be used very effectively.

The catalyst supports used in this step of the process according to the invention are generally porous solids, which are refractory oxides such as alumina, silica and silica alumina, magnesia, as well as titanium oxide and zinc oxide (here These latter oxides can be used alone or in combination with alumina or silica alumina). A preferred support is transitional alumina or silica having a specific surface area of 25 to 350 m ² / g. Naturally occurring compounds such as diatomaceous earth or kaolin are also suitable as support for the catalyst used in the process steps.

The catalyst is preferably used at least partially in its sulfurized form. This provides the advantage that the risk of hydrogenation of unsaturated compounds such as olefins or aromatic compounds at this starting stage is minimized. This sulfurization step may be performed using any technique known to those skilled in the art and is performed in situ.
Or ex situ.

The sulfur content of the catalyst after sulfiding is usually between 0.5 and 25% by weight, preferably between 4 and 20% by weight, and very preferably between 4 and 10% by weight. The purpose of the hydrodesulfurization carried out during this step is to saturate sulfur-containing compounds in gasoline that have already been preliminarily hydrogenated with sulfur unsaturated compounds at least once during step e). Is converted to H ₂ S. This makes it possible to obtain a distillate that meets the target standard in terms of sulfur-containing compound content. The gasoline obtained in this way shows only a slight decrease in octane number. This treatment aimed at decomposing the saturated sulfur-containing compound generated from step e) of the process is carried out in the presence of hydrogen, at least one selected from the group consisting of nickel, cobalt, iron, molybdenum, tungsten And a temperature of about 280 ° C to about 400 ° C, preferably about 290 ° C to about 380 ° C, more preferably 310 ° C to 360 ° C, and very preferably 320 ° C to 350 ° C, The pressure is generally about 0.5 to about 5 MPa, preferably 1 to 3 MPa, more preferably 1.5 to 3 MPa. Volumetric flow rate of the liquid is (expressed as volume of liquid per time per unit volume of the catalyst) from about 0.5 to about ^{10h -1,} preferably 1~8h ^-1. The H ₂ / HC (hydrocarbon) ratio is adjusted based on the target hydrodesulfurization rate, but is in the range of about 100 to about 600 liters / liter, preferably 100 to 300 liters / liter. All or part of this hydrogen is optionally obtained from step e) (unconverted hydrogen) or by recycling the hydrogen not consumed in steps a), b) or c). The embodiment of this second catalyst in this step makes it possible to decompose the saturated compounds contained in the distillate generated from step c) to H ₂ S under certain operating conditions. I found something. This embodiment makes it possible to achieve a high hydrodesulfurization level as a whole when the process steps according to the invention have been completed, and to minimize the decrease in octane number due to olefin saturation. The reason is that the conversion of olefins during step e) is usually limited to at most 20% by volume, preferably 10% by volume of olefins.

  In a specific embodiment, depending on the characteristics of the starting gasoline feedstock, in the latter the majority of its basic nitrogen-containing compounds are not present, but this is due to the sulfur present in the product generated from step b). Prior to step c) for alkylating at least a portion of the containing compound, it has been at least partially removed. In a preferred embodiment, this basic nitrogen-containing compound contained in the starting gasoline is at least partially removed prior to being introduced into step a) for hydrogenating the polyunsaturated compound. In most cases, in order to remove the basic nitrogen-containing compound, a treatment (washing) using an acidic aqueous solution is performed. Thus, if the starting gasoline contains a basic nitrogen-containing compound, the latter is at least partially removed by treatment with an acidic aqueous solution, which treatment is carried out in the product generated from step b). Carried out prior to step c) for alkylating at least part of the sulfur-containing compounds present in This washing is usually carried out before or after step a) in which the polyunsaturated compounds contained in the starting gasoline are selectively hydrotreated.

  The catalyst used in steps e) and f) is most often a separate sulfurized catalyst.

DESCRIPTION OF THE DRAWINGS (This is a schematic representation of an embodiment of the present invention and is not intended to limit the present invention)
Gasoline (α) containing a sulfur-containing compound, diolefin and olefin is injected into the pipe (1). Hydrogen is injected into the pipe (2) in such an amount that the hydrogen / diolefin molar ratio is greater than 1. This gasoline and hydrogen are contacted in a reactor (A) for selectively hydrogenating diolefins under conditions optimal for hydrogenating diolefins while suppressing olefin saturation. Let

The effluent from the reactor (A) is sent via line (3) to a unit (B) for increasing the weight of the sulfur-containing compound. The reaction carried out in this reactor (B) is substantially a reaction for increasing the weight of mercaptans having 1 to 6 carbon atoms and sulfides having 2 to 6 carbon atoms. Partial conversion of compounds such as CS ₂ and COS is also observed. The produced gasoline is introduced via a pipe (4) into a reactor (C) for increasing the weight of sulfur-containing compounds by adding to olefins. The sulfur-containing compound whose weight increases mainly in this reactor is a thiophene compound. In this reactor (C), olefin oligomerization reaction and partial alkylation of benzene compound are also observed. Therefore, the gasoline produced in the reactor (C) is heavier than gasoline (α), and light sulfur-containing compounds are removed. The gasoline produced in the reactor (C) is injected via a pipe (5) into a fractionation tower (D) that fractionates the gasoline into at least two fractions.

  Light gasoline having an end point of 55 ° C to 160 ° C is recovered from the top of the tower. This gasoline is desulfurized and does not require further processing. The final temperature of this light gasoline is determined by the maximum amount of sulfur allowed.

  The heavy gasoline recovered from the bottom of the tower is mixed with hydrogen introduced through the pipe (7) and through the pipe (8), and then sent to the desulfurization section (E + F). The starting point of distillation of this gasoline is 50 ° C to 130 ° C.

The hydrodesulfurization section (E + F) is designed so that gasoline can be desulfurized while suppressing olefin hydrogenation for the purpose of suppressing a decrease in octane number. This includes at least two reactors connected in series, the first reactor (E) of which saturates the thiophene-based compound and partially converts the sulfur-containing compound to H ₂ S. A catalyst system optimized for conversion is included. The second reactor contains a catalyst optimized to convert mercaptan to H ₂ S while suppressing hydrogenation of olefins present in gasoline. This desulfurization system is described in EP 1 077 247.

  Heavy gasoline recovered via the pipe (10) and light gasoline recovered via the pipe (6) can be mixed to produce completely desulfurized gasoline. Collect from pipe (11).

(Example 1 (comparative example))
The cracked gasoline is subjected to diolefin hydrotreating under conditions that convert the saturated sulfur-containing light compounds present in the feedstock to partially heavier compounds.

This treatment is carried out in a continuously operated reactor. This catalyst is of nickel and molybdenum type (a catalyst commercially available from Procatalyse Company as product number HR945). This reaction is carried out at a temperature of 180 ° C., a total pressure of 2.6 MPa, and a volumetric flow rate of 6 h ⁻¹ . The H ₂ / feed feed ratio is 10 expressed in liters of hydrogen per liter of feed feed.

The characteristics of the effluent after hydrogenation of catalytically cracked gasoline and diolefin and conversion of light compounds are shown in Table 1.

  In Table 1, MAV represents a maleic anhydride value. The same applies to the following tables.

When this treatment is completed, the gasoline is separated into two fractions, a light fraction in which distilled gasoline corresponding to a temperature of 100 ° C. corresponds to 65% by weight and a heavy fraction. This separation is carried out in a batch distillation column having 30 theoretical plates. The properties of the two fractions obtained are shown in Table 2.

  If the standard value for the sulfur content is greater than 60 ppm, the diolefin, mercaptan and sulfur content indicated by this light fraction can be used as is.

  This heavy gasoline should be desulfurized before use. In all cases, this system cannot produce desulfurized gasoline containing less than 40 ppm sulfur by recombining light and heavy gasoline.

(Example 2 (comparative example))
The catalytically cracked gasoline obtained after the hydrotreating of Example 1 is divided into two fractions, a light fraction in which distilled gasoline whose fraction point is equivalent to a temperature of 55 ° C. accounts for 20% by weight and a heavy fraction. Separate into minutes. This separation was carried out by using the same column as in Example 1. The properties of the two fractions obtained are shown in Table 3.

  The mercaptan, diolefin and sulfur exhibited by this light gasoline produced by distillation can be used as they are.

  This heavy gasoline needs additional desulfurization.

  Therefore, this heavy gasoline is subjected to hydrodesulfurization in a manner that uses a catalyst in an isothermal tube reactor.

The first catalyst (Catalyst A) is obtained by a “without excess solution” dry impregnation method, with a specific surface area of 130 m ² / g and a pore volume of 0.9 ml / g. An aqueous solution containing molybdenum and cobalt in the form of ammonium heptamolybdate and cobalt nitrate is used for the transition alumina formed into a spherical shape. The catalyst is then dried and calcined at 500 ° C. in an air atmosphere. Cobalt and molybdenum content of the catalyst, CoO 3%, a MoO ₃ 14%.

The second catalyst (Catalyst B) is prepared using 140 m ² / g transition alumina having a spherical shape with a diameter of 2 mm. The pore volume of the carrier is 1 ml / g. 1 kg of support is impregnated with 1 liter of nickel nitrate solution. The catalyst is then dried at 120 ° C. and then calcined in an air stream at 400 ° C. for 1 hour. The nickel content of this catalyst is 20% by weight. 100 ml of catalyst A and 200 ml of catalyst B are placed in two reactors connected in series so that the feedstock (heavy fraction) to be treated is first in contact with catalyst A and then with catalyst B. . A zone for sampling the distillate generated from step e) is provided between catalysts A and B. These catalysts are first contacted with a feedstock containing 2% by weight of sulfur in the form of dimethyl disulfide in n-heptane and subjected to a sulfiding treatment at a pressure of 3.4 MPa and a temperature of 350 ° C. for 4 hours.

The operating conditions for hydrodesulfurization are as follows: VVH = 1.33 h ⁻¹ (for all catalyst beds), H ₂ / hydrocarbon = 300 liters / liter, P = 2.0 MPa. The temperature of the catalyst zone containing the catalyst A is 280 ° C., whereas the temperature of the catalyst zone containing the catalyst B is 330 ° C.

The characteristics of the effluent thus obtained are shown in Table 4.

  This process, described in EP 1 077 247, makes it possible to produce a desulfurized gasoline whose mercaptan and diolefin content meets the level required for gasoline.

  In the specific case of this example, the desulfurization rate is 92.8%, the residual sulfur content is 25 ppm, and the decrease in octane number calculated from the formula of (RON + MON) / 2 is 2.75 points.

Example 3 (according to the invention)
Reactor for increasing the weight of sulfur-containing compounds by catalytically cracked gasoline obtained after the hydrotreatment of Example 1 (steps a) and b)) of the present invention by olefins (step in the present invention) c)). This step is carried out in a tubular reactor containing a phosphoric acid-based catalyst (catalyst C) supported on silica containing 20% by weight of phosphoric acid, the conditions being as follows: VVH = 1h ⁻¹ , Pressure = 2.0 MPa, temperature = 180 ° C. Before injecting into the reactor, isopropanol is added to the feed at a level of 500 ppm to continuously hydrate the catalyst in the reactor.

  The effluent thus produced is separated into two fractions using the distillation column described in Example 1. If the distillation fraction point is 100 ° C., the light fraction corresponds to 50% by weight of the starting gasoline.

Table 5 shows the characteristics of the gasoline produced in the alkylation step c) and the fractionation step d).

  If the total content of diolefins, mercaptans and sulfur in the light gasoline recovered at the outlet of this fractionation step is used, this gasoline can be used without further processing. This heavy gasoline requires a desulfurization process.

Desulfurization of heavy gasoline (steps e) and f)) of the process according to the invention is carried out in the apparatus described in Example 2. The operating conditions are as follows: VVH = 1.33 h ⁻¹ (for all catalyst beds), H ₂ / hydrocarbon = 300 liters / liter, P = 2.0 MPa. The temperature of the catalyst zone containing the catalyst A is 290 ° C., and the temperature of the catalyst zone containing the catalyst B is 340 ° C.

  The gasoline produced in this way shows only a sulfur content of 26 ppm or less. This can be used without additional processing. This gasoline is again merged with the light gasoline recovered in step d).

Table 6 shows the characteristics of desulfurized heavy gasoline and recombined gasoline.

  This system, implemented in accordance with the present invention, makes it possible to produce a desulfurized gasoline whose content of mercaptans and diolefins meets the level required for gasoline while suppressing the decrease in octane number.

  In the specific case of this example, the desulfurization rate is 92.6%, the residual sulfur content is 26 ppm, and the decrease in octane number calculated from the formula (RON + MON) / 2 is 2.15 points.

1 is a flow sheet schematically showing an embodiment of the present invention.

Explanation of symbols

A selective hydrogenation reactor B sulfur compound increase reactor C sulfur compound increase reactor D fractionator E hydrodesulfurization reactor F hydrodesulfurization reactor 1 starting gasoline piping 2 hydrogen piping 3 effluent piping 4 effluent Material piping 5 Outflow piping 6 Light fraction piping 7 Heavy fraction piping 8 Hydrogen piping 9 Outflow piping 10 Outflow piping 11 Desulfurized gasoline piping

Claims (14)

A process for producing a low sulfur content gasoline from a starting gasoline containing at least 150 ppm by weight of a sulfur containing compound, comprising at least the following steps:
At least one selected from the group consisting of platinum, palladium and nickel, for selectively hydrogenating non-aromatic, polyunsaturated compounds present in the starting gasoline in step a) In the presence of a catalyst comprising a Group VIII metal and a support, a pressure of 0.4 to 5 MPa, a volume flow rate ratio of 1 to 20 h ⁻¹ per hour of the liquid to be treated (feed feed volume per hour of catalyst volume) ), A process carried out at a temperature of 50 to 250 ° C. and a hydrogen to feed ratio of 1 to 50 liters / liter,
A step aimed at increasing the molecular weight of the light sulfur-containing product of at least one step b), the light sulfur-containing product being mainly present from the beginning in the gasoline introduced into step a) The presence of nickel-, platinum- or palladium-based catalysts which are contained in the products produced in step a) and / or mercaptans and sulfides having 1 to 6 carbon atoms in the molecule Below, the process is carried out under the conditions of a temperature of 100 to 300 ° C., a H ₂ / feed raw material ratio of 1 to 20 liters / liter, a volume flow rate ratio of ^{1 to} 10 h ⁻¹ , and a pressure of ^{1 to 3} MPa. And b) are carried out simultaneously in a single reaction zone comprising one or more catalyst beds of a single catalyst ,
A step for alkylating at least a part of said sulfur-containing compound of at least one step c), the sulfur-containing compound being mainly intended to obtain a sulfur-containing compound having a higher molecular weight b) In the form of a thiophene compound present in the product generated from the resin, zeolite, clay, functionalized silica or silicoaluminate with acidity, or graft with acidic functional groups In the presence of a catalyst comprising a catalyst substrate, the ratio of the feed raw material volume to be injected is 0.1 to 10 liter / liter / hour, the temperature is 10 to 350 ° C., the operating pressure is 0.1 to 3 MPa, and the olefin A step carried out under a condition of a molar ratio with respect to the thiophene compound being greater than 10 mol / mol,
At least one step d) for fractionating the gasoline generated from step c) into at least two fractions, the first fraction being substantially free of sulfur, during step c) The lightest olefin of the unconverted starting gasoline (light gasoline), at least one other fraction is heavier than the first fraction, rich in sulfur-containing compounds, and
To treat at least one of the heavier fractions generated from step d) on a catalyst which makes it possible to at least partially decompose the sulfur-containing compound of at least one step e) In the presence of a catalyst comprising at least one Group VIII element and / or at least one Group VIB element at least partially in the form of a sulfide, at a temperature of 210 ° C. to 350 ° C., a pressure 1 to 4 MPa, liquid volume flow rate ratio of 0.5 to about 20 h ⁻¹ (expressed as liquid volume per unit volume of catalyst per hour), and H ₂ / HC ratio of 100 to 600 liters / liter. A method comprising the steps of: A process for producing a low sulfur content gasoline from a starting gasoline containing at least 150 ppm by weight of a sulfur containing compound, comprising at least the following steps:
At least one selected from the group consisting of platinum, palladium and nickel, for selectively hydrogenating non-aromatic, polyunsaturated compounds present in the starting gasoline in step a) In the presence of a catalyst comprising a Group VIII metal and a support, a pressure of 0.4 to 5 MPa, a volumetric flow rate ratio of 1 to 20 h of liquid to be treated per hour ^-1 (Feed feed volume per catalyst volume per hour), temperature 50 to 250 ° C., and a process performed under conditions of hydrogen to feed feed ratio 1 to 50 liters / liter,
A step aimed at increasing the molecular weight of the light sulfur-containing product of at least one step b), the light sulfur-containing product being mainly present from the beginning in the gasoline introduced into step a) The presence of nickel-, platinum- or palladium-based catalysts which are contained in the products produced in step a) and / or mercaptans and sulfides having 1 to 6 carbon atoms in the molecule Below, temperature 100-300 ° C, H ₂ / Feed feed ratio 1-20 liters / liter, volumetric flow rate ratio 1-10 h ^-1 And a step performed under conditions of a pressure of 1 to 3 MPa, and all or part of the gasoline hydrogenated in step a) is flowed over the catalyst in step b),
A step for alkylating at least a part of said sulfur-containing compound of at least one step c), the sulfur-containing compound being mainly intended to obtain a sulfur-containing compound having a higher molecular weight b) In the form of a thiophene compound present in the product generated from the resin, zeolite, clay, functionalized silica or silicoaluminate with acidity, or graft with acidic functional groups In the presence of a catalyst comprising a catalyst substrate, the ratio of the feed raw material volume to be injected is 0.1 to 10 liter / liter / hour, the temperature is 10 to 350 ° C., the operating pressure is 0.1 to 3 MPa, and A step carried out under a condition of a molar ratio with respect to the thiophene compound being greater than 10 mol / mol,
At least one step d) for fractionating the gasoline generated from step c) into at least two fractions, the first fraction being substantially free of sulfur, during step c) The lightest olefin of the unconverted starting gasoline (light gasoline), at least one other fraction is heavier than the first fraction, rich in sulfur-containing compounds, and
To treat at least one of the heavier fractions generated from step d) on a catalyst which makes it possible to at least partially decompose the sulfur-containing compound of at least one step e) In the presence of a catalyst comprising at least one Group VIII element and / or at least one Group VIB element at least partially in the form of a sulfide, at a temperature of 210 ° C. to 350 ° C., a pressure 1 to 4 MPa, liquid volume flow ratio 0.5 to about 20 h ^-1 (Expressed in volume of liquid per unit volume of catalyst per hour), and H ₂ / HC ratio 100-600 liters / liter of the process implemented. Treating at least one of said heavier fractions separated in step d) on a catalyst which makes it possible to at least partially decompose sulfur-containing compounds; The catalyst is formed under a condition that suppresses hydrogenation, and the catalyst comprises a combination of cobalt and molybdenum, and the molybdenum density in the catalyst (weight percent of MoO ₃ per unit surface area) is greater than 0.07. There, the specific surface area of the catalyst is less than 190 m ² / g, a method according to claim 1 or 2. It is possible to at least partially decompose the sulfur-containing compounds that were not converted during step e) while suppressing hydrogenation of olefins without removing the H ₂ S produced during step e). A process comprising at least one step f) for treating the product obtained in step e) on and under a catalyst to be selected from the group consisting of nickel, cobalt, iron, molybdenum, tungsten In the presence of a catalyst containing one basic metal, a temperature of 280 ° C. to 400 ° C., a pressure of 0.5 to 5 MPa, a liquid volume flow rate (expressed as a volume of the liquid per unit volume of the catalyst) 0.5 The method according to one of claims 1 to 3 , which is carried out under conditions of 10 to 10 h ^-1 and an H ₂ / HC (hydrocarbon) ratio of 100 to 600 liters / liter. The process according to one of claims 1 to 4 , wherein the starting gasoline is a catalytically cracked gasoline whose final boiling point is 120C to 230C.   A basic nitrogen-containing compound from which said starting gasoline is at least partially removed prior to step c) for alkylating at least some of the sulfur-containing compounds present in the product generated from step b); The method according to claim 1, wherein the removal of the basic nitrogen-containing compound is carried out by treatment with an acidic aqueous solution.   The basic nitrogen-containing compound contained in the starting gasoline is at least partially removed before the starting gasoline is introduced into step a) for hydrogenating polyunsaturated compounds. 6. The method according to 6.   8. A process according to claim 3 wherein the desulfurized heavy gasoline generated from step f) is subjected to a stripping treatment by means of a cover gas which covers and protects it from chemical changes. .   A process according to one of claims 3 to 8, wherein steps e) and f) are carried out in at least two consecutive, separate reaction zones.   10. The light gasoline generated from step d) and at least a part of the heavy gasoline generated from step f) are mixed to form desulfurized gasoline as a whole. the method of.   The process according to one of claims 3 to 10, wherein the catalyst used in steps e) and f) is a separate sulfurized catalyst.   12. The process according to claim 3, wherein steps e) and f) are carried out in two reactors arranged in series, and the effluent from the first reactor is treated together in the second reactor. The method described.   2. The heavy fraction generated from step d) is sent to a fractionation zone which makes it possible to obtain a heavy fraction enriched with sulfur and a lighter fraction with less sulfur. 13. The method according to 1 to 12.   The gasoline generated from the hydrodesulfurization in step e) or f) is sent to a fractionation zone that makes it possible to obtain a heavy fraction with a high sulfur content and a lighter fraction with a low sulfur content. 13. A method according to claim 3 to 12.

Images