FR2837831A1 - Production of hydrocarbons low in sulfur and mercaptans comprises two-stage catalyzed hydrodesulfurization with intermediate separation of hydrogen sulfide, for obtaining ultra-low sulfur petrol fuels - Google Patents

Abstract

Desulfurization involves catalytic hydrodesulfurization giving a 90% rate of desulfurization, the separation of most of the hydrogen sulfide from the effluent, and a second hydrodesulfurization in conditions giving a degree of desulfuration lower than the primary stage. An Independent claim is also included for the applications of the process.

Description

to this product in a composition / water ratio of about 1.

  The present invention relates to a process for producing low sulfur hydrocarbons. This hydrocarbon fraction contains an olefin fraction generally greater than 5% by weight and most often greater than 10% by weight. The method makes it possible in particular to valorize the entirety of a sulfur-containing gasoline cut by reducing the sulfur and mercaptan contents of said gasoline cut to very low levels, without reducing the gasoline yield, and by minimizing the reduction of the gasoline fraction. octane number during the process. The invention is particularly applicable when the gasoline to be treated is a catalytic cracking gasoline containing a sulfur content greater than 500 ppm by weight or even greater than 1000 ppm by weight or even 2000 ppm by weight, and when the desired sulfur content in the Desulphurized gasoline is less than 50 ppm by weight, or even 20

ppm weight or even 10 ppm weight.

Prior art.

  Future specifications for motor fuels include a significant reduction in the sulfur content of these fuels, including gasoline. This reduction is intended to limit, in particular the content of sulfur oxide in the automobile exhaust gas. Current specifications for sulfur levels are in the order of 150 ppm by weight and will decrease in the coming years to

  reach levels below 10 ppm after a transition to 30 ppm weight.

  The evolution of sulfur content specifications in fuels thus requires

  the development of new processes for the deep desulphurisation of species.

  The main sources of sulfur in gasoline bases are the so-called cracking gasoline, and mainly the gasoline fraction resulting from a process for the catalytic cracking of a residue from the atmospheric or vacuum distillation of a crude oil. The gasoline fraction from catalytic cracking, which represents on average 40% of gasoline bases, contributes more than 90% to the sulfur input in gasoline. Therefore, the production of low sulfur species requires a step of desulfurization of catalytic cracking gasolines. This desulfurization is conventionally carried out by one or more steps of contacting the sulfur compounds contained in said gasolines with a gas rich in

  hydrogen in a so-called hydrodesulfurization process.

  In addition, the octane number of such species is very strongly related to their olefin content. Preserving the octane number of these species therefore requires limiting the transformation reactions of olefins into paraffins which are inherent in

hydrodesulfurization processes.

  In addition, the species have corrosive properties due to the presence of mercaptans. In order to limit the corrosivity of gasolines, it is generally necessary to lower the mercaptan content to values of at least less than 10 ppm and ideally 5 ppm. The mercaptans measured in the desulfurized gasolines are so-called recombination mercaptans, ie derived from the addition reaction of the hydrogen sulphide (H 2 S) produced in the course of the desulphurization step and the olefins. present in the essence. The solution usually used to eliminate

  these mercaptans consists of hydrogenating the olefins present in the gasoline.

  However, for the reasons already described, this hydrogenation leads to a loss

  of unacceptable octane on catalytic cracking gasolines.

  Numerous solutions have been proposed for selectively removing sulfur compounds in gasolines by limiting the undesirable hydrogenation reactions of olefins, generally evaluated by those skilled in the art in the form of an olefin saturation rate at the outlet of the reactor. Among these methods, one can distinguish the processes in which the gasoline is treated in one or two reactors in series without intermediate separation of H2S. These methods make it possible to partially solve the problem of the octane number and mercaptans on fillers which contain a sulfur content which does not generally exceed 1000 ppm, and for which

  Desulfurization rates are low, typically less than 90%.

  The treatment of sulfur-rich gasolines (ie containing more than 1000 ppm or more than 2000 ppm of sulfur) with a view ultimately to reaching sulfur contents of less than 50 ppm, or even 20 ppm or even 10 ppm, can optionally and preferably require the implementation of a process comprising a hydrodesulfurization in at least two hydrodesulphurization reactors in series, and an intermediate removal of H2S formed during the first hydrodesulfurization step. This type of scheme is preferably intended to achieve high desulphurization rates, for example 99% to bring a gasoline with sulfur concentrations of the order of 2000 ppm to concentrations

in sulfur of the order of 10 ppm.

  For example, EP 0755995 proposes a scheme consisting of at least two hydrodesulfurization stages and a step of removing the H2S between two hydrodesulfurization reactors. The hydrodesulfurization rate must be understood, at each step, between 60% and 90%. Such a method does not however allow to consider achieving desulfurization rates greater than 99% on an industrial scale. To reach a deeper desulfurization, it appears necessary to add at least one step

  This greatly limits the economic attractiveness of the process.

  US Pat. No. 6,231,753 proposes the treatment of highly sulphurous species by a scheme also comprising 2 hydrodesulfurization steps and an intermediate elimination of the H 2 S formed. The operating conditions are such that the rate and the desulphurization temperature of the essences of the second hydrodesulfurization step

  are superior to those of the first step.

Summary of the invention.

  In general terms, the present invention relates to a new process comprising two hydrodesulphurization steps and an intermediate removal of H2S which makes it possible: - to reach the future specifications on the gasolines for automobile, that is to say sulfur contents of the order of 30 ppm or even 10 ppm depending on the country, - to control the processes of hydrogenation of olefins during said process, - to limit the loss of octane number for the hydrodesulfurization processes, to reduce the mercaptans content for sulfur and olefins content

  data in desulfurized gasoline.

  More specifically, the invention relates to a process for the desulphurization of a hydrocarbon fraction comprising sulfur compounds and olefinic compounds comprising at least the following successive steps: - first desulfurization in the presence of hydrogen and a hydrodesulphurization catalyst under conditions leading to a desulfurization rate of said section strictly greater than 90%, - a separation of most of the hydrogen sulphide (H2S) effluents from the first desulfurization, - a second desulphurization effluents, freed of hydrogen sulphide and resulting from the separation step, in the presence of hydrogen and a hydrodesulfurization catalyst and under conditions leading to a desulfurization rate

  said effluents lower than that of the first desulfurization.

  Thus, the present desulfurization process provides a solution for achieving high desulphurization rates, typically greater than 95% and more specifically greater than 99%, while limiting the octane loss by hydrogenation of olefins, as well as the formation of mercaptans. recombination. This results in the production of a gasoline

  low in sulfur and mercaptans and high octane.

  Detailed description of the invention.

  The invention relates to a process for the desulfurization of a hydrocarbon fraction comprising sulfur compounds and olefinic compounds comprising at least the following successive stages: A first desulfurization in the presence of hydrogen and a hydrodesulphurization catalyst under conditions leading to a desulfurization rate of said cut strictly greater than 90%, - a separation of most of the hydrogen sulphide (H2S) effluents from the first desulphurization, - a second desulphurization of effluents, freed from sulphide of hydrogen and from the separation step, in the presence of hydrogen and a hydrodesulphurization catalyst and under conditions leading to a desulfurization rate

  said effluents lower than that of the first desulfurization.

  In the process according to the invention preferably at least one of the hydrodesulphurization catalysts comprises at least one element from the group Vlil of the periodic table and more preferably at least one of the catalysts comprises in part

  in addition to at least one element of group VIB of the Periodic Table.

  Very preferably, said hydrodesulphurization catalysts comprise at least one element of the Vlil group of the classification chosen from the group consisting of nickal and cobalt and at least one element from group VIB of the classification.

  selected from the group consisting of molybdenum and tungsten.

  Preferably, the first desulphurisation of the process according to the invention is carried out at a temperature of between 250 ° C. and 350 ° C., at a pressure of between 1 and 3 MPa, at a liquid hourly space velocity of between 1 hr and 4 hr. with an H2 / HC ratio of between 501/1 and 5001 / l and preferably the second desulfurization is carried out at a temperature of between 200 ° C. and 300 ° C., at a pressure of between 1 and 3 MPa, at a liquid hourly space velocity between 1h 'and

  1 Oh-4 and with an H2 / HC ratio of between 50 l / l and 500 l / l.

  Preferably, the desulfurization rate of the second desulphurization is strictly greater than 80% and more preferably, the difference between the desulfurization rates of the first and second desulfurization is at least one percent in absolute value. Such a difference can be obtained in particular by virtue of a difference in temperature eVou of hourly volume velocity between the first and the second desulfurization, eVou via a catalytic activity different from the catalysts used in the first and second hydrodesulphurization step, for example due to of a difference in the composition or the preparation of these catalysts. The process according to the invention may optionally also comprise an additional step of selective hydrogenation of the diolefins contained in the hydrocarbon fraction, said step being carried out before the first desulfurization. It may more preferably also comprise an additional step of increasing the weight of the light sulfur compounds, said step being carried out before the first desulfurization, and very preferably further comprising at least one additional step of separating said cut in at least two fractions including: - a light fraction containing a minor portion of the sulfur compounds, - a heavy fraction containing the majority of the sulfur compounds, at least said heavy fraction being then treated according to the first desulphurization step. The process according to the invention is preferably applied to fillers such as gasoline cuts resulting from catalytic cracking or the coking of a filler.

  heavy hydrocarbon or steam cracking.

  The invention will be better understood on reading the following embodiment, donated to

  purely illustrative and non-limiting of the invention.

  According to the preferred but non-mandatory embodiment of the invention which follows, the feedstock to be desulphurised is optionally optionally treated in a series of reactors for the selective hydrogenation of diolefins (step a) and for increasing the weight of light sulfur compounds ( step b). The feed thus pretreated is then distilled and fractionated into at least two cuts (step c): a light gasoline low in sulfur and rich in olefins and a heavy gasoline rich in sulfur and depleted in olefins. The light fraction obtained from the previous three stages generally contains less than 50 ppm of sulfur, preferably less than 20 ppm of sulfur, and very preferably less than 10 ppm of sulfur, and generally does not require any subsequent treatment. before incorporation as a gasoline base. The heavy fraction resulting from the previous three stages, which concentrates most of the sulfur, is treated according to the process that is the subject of the present invention. This preferred embodiment has the advantage of further minimizing the octane loss since the light olefins with 5 carbon atoms, which are easily hydrogenated, are not

  sent to the hydrodesulfurization section.

  In general, the experimental conditions of these pretreatment steps a), b) and c) are as follows: 1) Selective Hydrogenation (Step a): This optional pre-treatment step of the gasoline to be desulfurized is intended to

  at least partially remove the diolefins present in the gasoline.

  The hydrogenation of the dienes is an optional but advantageous step which makes it possible to eliminate practically all the dienes present in the section to be treated before the hydrotreatment. Diolefins are precursors of gums that polymerize

  in hydrotreating reactors and limit their service life.

  This step generally takes place in the presence of a catalyst comprising at least one Group V111 metal, preferably selected from the group consisting of platinum, palladium and nickel, and a support. For example, a catalyst containing 1 to 20% by weight of nickel deposited on an inert support, such as, for example, alumina, silica, silica-alumina, a nickel aluminate or a support containing at least 50% alumina. This catalyst generally operates at a pressure of 0.4 to 5 MPa, at a temperature of 50 to 250 C, with a liquid hourly space velocity of 1 hr-4 to 10 hr. Another metal of the group VIb may be combined to form a bimetallic catalyst, such as, for example, molybdenum or tungsten. This metal of group Vlb, if it is associated with the metal of group Vlil will be

  deposited at a level of 1% by weight at 20% by weight on the support.

  The choice of operating conditions is particularly important. It will operate most generally under pressure in the presence of a quantity of hydrogen in small excess

  relative to the stoichiometric value necessary to hydrogenate the diolefins.

  The hydrogen and the feedstock to be treated are injected in ascending or descending streams into a reactor preferably with a fixed bed of catalyst. The temperature is most generally between 50 and 300 C, and preferably between 80 and 250 C, so

  more preferred between 120 and 210 C.

  The pressure is chosen to be sufficient to maintain more than 80%, and preferably more than 95%, by weight of the gasoline to be treated in the liquid phase in the reactor; it is most generally from 0.4 to 5 MPa and preferably greater than 1

  MPa. An advantageous pressure is between 1 to 4 MPa inclusive.

  The space velocity is. under these conditions of the order of 1 to 12 h-4, preferably

the order of 4 to 10 h-.

  The light fraction of the catalytic cracking gasoline fraction can contain up to a few% by weight of diolefins. After hydrogenation, the diolefin content is reduced to less than 3000 ppm, even less than 2500 ppm and better to less than 1500

  ppm. In some cases, a diene content of less than 500 ppm can be obtained.

  The diene content after selective hydrogenation can even be reduced in

some cases less than 250 ppm.

  Concomitantly with the selective hydrogenation reaction of the diolefins, there is an isomerization of the double bond of the external olefins leading to the formation of internal olefins. This isomerization has the effect of forming olefins more refractory to saturation with hydrogen and lead to a slight gain in the number of octane (or a compensation of the octane number due to the low olefin loss). This is probably due to the fact that internal olefins have a subscript

  octane generally higher than that of terminal olefins.

  According to one embodiment of the invention, the step of hydrogenation of the dienes takes place in a catalytic hydrogenation reactor which comprises at least one catalytic reaction zone generally traversed by the entire charge and by the

  amount of hydrogen needed to effect the desired reactions.

  2) Weighting of light sulfur compounds (step b): This optional step consists of converting the light compounds of saturated sulfur, that is to say compounds whose boiling point is lower than that of thiophene, into compounds saturated sulfur whose boiling temperature is higher than that of thiophene. These light sulfur compounds are typically mercaptans of 1 to 5 carbon atoms, CS2 and sulfides comprising 2 to 4 carbon atoms. This transformation is preferably carried out on a catalyst comprising at least one element of the Vlil group (groups 8, 9 and 10 of the new periodic classification) on a support of alumina, silica or silica alumina or nickel aluminate type. The choice of the catalyst is made in particular so as to promote the reaction between lagers mercaptans and olefins, which leads to

  mercaptans or sulphides with higher boiling points than thiophene.

  This optional step may be carried out at the same time as step a), on the same catalyst. For example, it may be particularly advantageous to operate, during the hydrogenation of diolefins, under conditions such that at least

  a part of the compounds in the form of mercaptans are converted.

  In this case the temperatures are generally between 100 and 300 C and preferably between 150 and 250 C. The H2 / load ratio is adjusted to between 1 and 20 liters per liter, preferably between 3 and 15 liters per liter. The space velocity is generally between 1 and 10 h -1, preferably between 2 and 6 h -1 and the pressure between

  0.5 and 5 MPa, preferably between 1 and 3 MPa.

  3) separation of the essence into at least two fractions (step c): This step is optional. When it is carried out after steps a) and b), it makes it possible to produce a light desulfurized gasoline, most often containing less than ppm mercaptans. During this step, the gasoline is fractionated into at least two fractions: a light fraction having a limited residual sulfur content, preferably less than about 50 ppm, preferably less than about 20 ppm, very preferably less than about 10 ppm, and allowing to use this cup without performing other (s) treatment (s) to reduce its sulfur content, - a heavy fraction in which the major part of the sulfur, that is to say all of the sulfur initially present in the feed and not found in gasoline

light, is concentrce.

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

the initial essence.

  The light gasoline obtained after the separation generally contains at least all of the five-carbon olefins, preferably the five-carbon compounds.

  carbon atoms and at least 20% of the six-carbon olefins.

  Generally, this light fraction obtained after steps a) and b) has a low sulfur content, ie it is not generally necessary to treat the

  light cut before using as fuel.

  The gasoline treated using the variant of the process according to the invention which is described below is a cracking gasoline directly from the cracking unit or

  pretreated according to at least one of the steps a), b) or c) described above.

  The process according to the invention comprises two stages d) and f) of unfused ratio carried out in two separate reaction zones, as well as a step e) of separating the H2S.

  between the two hydrodesulfurization zones.

  The first hydrodesulfurization step (step d) consists in passing the gasoline to be treated in the presence of hydrogen, on a hydrodesulfurization catalyst, at a temperature of between 250 ° C. and 350 ° C., preferably between 270 ° C. and 320 ° C. C and at a pressure of between 1 and 3 MPa, preferably between 1.5 and 2.5 MPa. The liquid space velocity is generally between 1 hr-4 and 10 hr -1, preferably between 2 hr-4 and 5 hr, the ratio H 2 / HCl is between 50 liters / liter (l / l) and 500 l / l. preferably between 100 l / l and 400 l / l, and more preferably between 150 l / l and 300 l / l. The ratio H2 / HC is the ratio between the hydrogen flow rate under 1 atmosphere and 0 C and the hydrocarbon flow rate. Under these conditions, the reaction takes place in the gas phase. The desulfurization rate achieved during this step is strictly greater than 90%, ie, for example, a gasoline initially containing 2000 ppm of sulfur will be converted into a gasoline containing less than 200 ppm of sulfur. The operating conditions during this step are therefore adjusted according to the characteristics of the feedstock to be treated to reach a desulfurization rate strictly greater than

  %, more preferably greater than 92% and most preferably greater than 94%.

  The effluents resulting from this first hydrodesulfurization stage are partially desulphurized gasoline, residual hydrogen and H2S produced by decomposition of

sulfur compounds.

  This step is followed by a separation step (step e) of most of the H2S of the other effluents. This step is intended to remove at least 80% and preferably at least 90% of the H 2 S produced under step d). The elimination of H2S

  can be performed in different ways, for the most part known to those skilled in the art.

  For example, the absorption of H 2 S by a metal oxide mass, preferably selected from the group consisting of zinc oxide, copper oxide or molybdenum oxide. This absorbent mass is preferably regenerable and can be regenerated continuously or discontinuously by means of, for example, a heat treatment in an oxidizing or reducing atmosphere. The adsorbent mass can be used in fixed bed or moving bed. Another more traditional method is to

  cooling the effluent of step d) to produce a liquid and a gas rich in H2 and H2S.

  H2S can be separated from H2 by means of an amine wash unit whose

  operation is well known to those skilled in the art.

  A second desulfurization step f 1 is intended to carry out a deep desulphurization of the gasoline resulting from stage e) up to the desired sulfur content. This step consists in passing over a hydrodesulphurization catalyst, the gasoline resulting from stage e) mixed with hydrogen at a temperature of between 200 ° C. and 300 ° C., preferably between 240 ° C. and 290 ° C., at a pressure of between 1 and 3 MPa, preferably between 1.5 and 2.5 MPa. The liquid space velocity is generally between 1 hr-4 and 10 hr-4, preferably between 2 hr and 8 hr-4, the ratio H 2 / HCl is between 50 liters / liter (l / l) and 500 I / l, preferably between 100 l / l and 400 l / l, and more preferably between 1501 / l and 3001 / l. Under these conditions, the reaction takes place in the gas phase. The mixture of gasoline and hydrogen treated in this step contains less than 100 ppm of H2S and preferably less than 50 ppm of H2S. The operating conditions of this stage are such that the desulphurization rate makes it possible to reach the required sulfur content, while maintaining a lower desulphurization rate than that of the first stage. The charge to be treated during this step is much less sulfurous than the initial charge, and the desired desulphurization rates are lower. Therefore, the necessary catalyst volumes as well as the operating temperatures are also lower. For example, the WH (hourly volume velocity) of the desulphurization step fl may be 1.5 times greater than the WH of step d), eWh the temperature of the desulfurization step fl may be, for example, less than at least 10 C and advantageously at least 20 C to that of step d). Most often, the catalyst volumes are fixed on the industrial units, the desulfurization rate of the fl step is then mainly adjusted by the temperature. However, said difference can be adjusted, without departing from the scope of the invention, by means of any parameter known to act on the desulfurization rate of each step d) or 9, for example using to perform step 9 a less active catalyst than that of step d). The difference in activity between the catalysts of steps d) and f1 can for example be obtained by using, for step 0, a catalyst containing a lower amount of metals or a lower specific surface support compared to the catalyst of the invention. step d). Another solution may be to use a partially deactivated catalyst in step f1. The operating conditions during step f1 are therefore adjusted as a function of the characteristics of the feedstock to be treated in order to reach a desulphurization rate that is usually strictly greater than 80%, preferably more than 85% and so

  very preferred greater than 92%, or even greater than 95%.

  The difference between the desulfurization rates of the first and the second hydrodesulphurization step is generally greater than 1 percent, preferably greater than 2 percent, and most preferably greater than 3 percent.

absolute value.

  Surprisingly, it has indeed been found by the applicant that such constraints on the respective desulfurization rates of steps d) and f) make it possible to minimize the mercaptan content of the gasoline produced, and thus make it optional.

  or less restrictive any subsequent step of softening the essence.

  According to an alternative embodiment of the present process it is also possible to inject into the second hydrodesulfurization reactor fresh hydrogen, to separate the hydrogen from the gasoline produced and to inject this hydrogen which contains

  generally less than 200 ppm of H2S in the first stage of hydrodesulfurization.

  The catalysts used in steps d) and f) comprise at least one element

  group Vlil eVou at least one element of group VIB on a suitable support.

  The metal content of the Vlil group, expressed as oxide, is generally between 0.5 and 15% by weight, preferably between 1 and 10% by weight. The metal content of group VIB is generally between 1, 5 and 60% by weight, preferentially

between 3 and 50% weight.

  The element of group V111, when present, is preferably cobalt, and the element

  Group VI B. When present, is usually molybdenum or tungsten.

  The catalyst support is usually a porous solid, such as for example an alumina, a silica-alumina or other porous solids, such as, for example, magnesia, silica or titanium oxide, alone or in mixture with alumina or silica-alumina. In order to minimize the hydrogenation of the olefins present in the heavy gas, it is advantageous to preferentially use a catalyst in which the molybdenum density, expressed in% by weight of MoO 3 per unit area, is greater than 0.07 and preferably greater than 0.07. 0.10. The catalyst according to the invention preferably has a specific surface area of less than 190 m 2 / g, more preferably

  preferred less than 180 m 2 / g, and very preferably less than 150 m 2 / g.

  After introduction of the element or elements and possibly shaping of the catalyst (when this step is performed on a mixture already containing the base elements), the catalyst is in a first activated step. This activation can correspond to either an oxidation then a reduction, a direct reduction, or a calcination only. The calcination step is generally carried out at temperatures ranging from about 100 to about 600 C and preferably between

and 450 C under a flow of air.

  The catalyst is preferably used at least in part in its sulfurized form.

  The introduction of sulfur may occur before or after any activation step, that is to say calcination or reduction. Preferably, no catalyst oxidation step is performed when the sulfur or a sulfur compound has been introduced on the catalyst. The sulfur or a sulfur compound may be introduced ex situ, that is to say outside the reactor where the process according to the invention is carried out, or in situ, that is to say in the reactor used for process according to the invention. In the latter case, the catalyst is preferably reduced under the conditions described above, then sulfided by passing a feed containing at least one sulfur compound, which once decomposed leads to the fixation of sulfur on the catalyst. This charge can be gaseous or liquid, for example hydrogen containing H2S, or a liquid

  containing at least one sulfur compound.

  The interest and the advantages of the present invention are demonstrated by the comparison of Examples 1 and 2 according to the prior art and of Example 3, in accordance with the invention. Exemule 1 (according to the prior art): Example 1 relates to a desulfurization process without intermediate elimination

  H2S and with a hydrodesulfurization step.

  A hydrated sulphurization catalyst A is obtained by impregnating "without excess solution" of a transition alumina in the form of beads 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. The catalyst is then dried and calcined under air at 500 C. The content

  The cobalt and molybdenum content of this sample is 3% CoO and 10% MoO3.

  1 ml of catalyst A are placed in a fixed bed tubular hydrodesulphurization scavenger. The catalyst is first sulphurized by treatment for 4 hours under a pressure of 3.4 MPa at 350 ° C., in contact with a constituse charge of 2% of sulfur.

  as dimethyl disulphide in n-heptane.

  The treated feedstock is a catalytic cracked gasoline with an initial boiling point of 50 ° C and an end point of 225 ° C. Its sulfur content is 2000 ppm by weight and its bromine number (bw) is 69 g. 100 g, which corresponds,

  approximately 36% by weight of olefins.

  This feedstock is treated on catalyst A at a pressure of 2 MPa bar, an H2 / HC ratio of 3001 / l and a VVH of 2 h-. Table 1 shows the influence of the

  temperature on the desulfurization rate and saturation of the olefins.

Table 1

  Temperature Content in Content of (C) Mercaptan Sulfur Desulfurization Rate Gasoline Sulfurization (ppm) (%) desulfurized olefin (HDO) (pPm)

310 41 32 97.9 20.3 70.6

320 23 20 98.8 14.7 78.7

330 12 11 99.4 10 85.5

  The operating conditions required to reach 10 ppm of sulfur with this type

  High sulfur content gasoline is a high temperature (> 310 C) and a low WH (2 h-).

  Under these conditions, it is possible to reach desulfurization rates greater than 99%, but the saturation rate of the olefins then becomes very high (greater than

  85%), which is detrimental to the octane number.

  Example 2 (According to the Prior Art) Example 2 relates to a desulfurization process with two hydrodesulphurization stages and the intermediate elimination of the H 2 S formed, in accordance with the prior art. Catalyst A is operated under milder conditions than those of Example 1. According to the prior art, the desulfurization rate of the second hydrodesulfurization step is higher than that of the first step. The treated load

  is the same as the load of Example 1.

  The feedstock is sent to the reactor of Example 1 over Catalyst A mixed with hydrogen. The operating temperature is 285 ° C. The other operating conditions are specified in Table 2. The effluents leaving the reactor contain 239 ppm of sulfur. They are cooled and stripped to separate hydrogen and H2S from the hydrocarbon phase. The stripped effluents are then re-injected into the reactor charged with the catalyst A mixed with fresh hydrogen, according to the operating conditions of said second stage indicated in Table 2. The charge flow rate has been multiplied by 1.5 with respect to flow of the first step. The experimental setup used includes an in-line sulfur analyzer that continuously measures the sulfur content in the effluents. The reactor temperature at the second stage was adjusted to produce a gasoline containing 10 ppm sulfur.

Table 2

  First step _ Temperature 1 C 285 WH 1 h-1 4 Pressure 1 Bar 20

H2 / HC 1 - 300

  Sulfur output ppm 239 IBr output 49.9

HDS% 88.1

  Second step Temperature 2 C 292 _ WH 2 h-1 6 Pressure 2 Bar 20

H2 / HC 2 1/1 300

  Sulfur at output ppm 10 Mercaptans in ppm 9 output IBr output = 36.9

H DS% 96.0

  This example shows that the process comprising two hydrodesulfurization steps with intermediate removal of the H 2 S is much more selective than the one-step process employed in Example 1. Indeed, the gasoline produced in Example 2 has the same sulfur content as the gasoline of Example 1, but the saturation rate of olefins (HDO) is here 46.7% against 85.5%. % for example 1. The method implemented according to example 2 thus makes it possible to minimize the processes

  leading to the saturation of olefins during hydrodesulfurization.

  Example 3 According to the Invention In this example, the desulfurization rate of the first stage is on the contrary of

  Example 2 is superior to that of the second step.

  The treated batch is the same as that of Examples 1 and 2.

  The feed is sent to the reactor previously described on catalyst A in a mixture with hydrogen. The operating temperature is 300 ° C. The other operating conditions are specified in Table 3. The effluents leaving the reactor respectively contain 117 ppm of sulfur. The procedure is the same as for example 2: the effluents are cooled and stripped in order to separate the hydrogen and the H 2 S from the hydrocarbon phase which is reinjected into the reactor charged with catalyst A, mixed with the According to the operating conditions indicated in Table 3, the charge rate was multiplied by 1.5 with respect to the flow rate of the first desulfurization stage. As in Example 2, the temperature was adjusted so as finally to recover at the outlet of the reactor a

gasoline containing 10 ppm sulfur.

Table 3

  First step Temperature 1 'C 300

WH 1 1- 4

Pressure 1 MPa 2 _

H2 / HC 1 1/1 300

  Sulfur at the exit pm r 117. IBr output 43.4

H DS% 94.2

  Second step Temperature 2 C 264 VVH 2 h- 6 Pressure 2 MPa

H2 / HC 2 _ 300

  Sulfur output ppm 10 Mercaptans output ppm 6 IBr output 36.8

HDS% 91.2

  Overall HDS% 99.5 overall HDO% 46.7 The process according to the invention, that is to say the implementation of a desulphurization rate of the first stage higher than that of the second stage makes it possible to reach the same sulfur content in the desulphurized gasoline, as well as the same degree of saturation of the olefins as the prior art, illustrated by Example 2. However, the effluent produced by the process according to the invention comprises 30 % less mercaptans than the gasoline obtained from Example 2. The implementation of the process according to the present invention thus makes it possible not only to strongly limit the saturation of the olefins, but also to greatly reduce the mercaptan content. and therefore the corrosiveness of

the essence produced.

Claims (12)

  1. A process for desulfurizing a hydrocarbon fraction comprising sulfur compounds and olefinic compounds comprising at least the following successive stages: a first desulfurization in the presence of hydrogen and of a hydrodesulphurization catalyst under conditions leading to a desulfurization rate of said cut strictly greater than 90%, - a separation of most of the hydrogen sulphide effluents from the first desulphurization, - a second desulphurization of effluents, freed of hydrogen sulphide and resulting from the separation step, in the presence of hydrogen and a hydrodesulfurization catalyst and under its conditions leading to a rate of   desulfurization of said effluents lower than that of the first desulfurization.   The process according to claim 1 wherein at least one of the hydrodesulphurization catalysts comprises at least one member of the group Vlil of the periodic classification.   3. The process according to claim 2 wherein at least one of the catalysts further comprises at least one Group VIB element of the Periodic Table. 4. Method according to claim 1 comprising at least one element of the group V111 of the classification selected from the group consisting of nickel and cobalt and at least at least one element of group VIB of the classification chosen from the group   consisting of molybdenum and tungsten.   5. Method according to one of the preceding claims wherein the first   desulfurization is carried out at a temperature of between 250 ° C. and 350 ° C., under a pressure of between 1 and 3 MPa, at a liquid hourly space velocity   between 1 h-4 and 1 Oh-4 and with an H2 / HC ratio of between 50 1/1 and 500 1/1.   6. Method according to one of the preceding claims wherein the second   desulfurization is carried out at a temperature of between 200 ° C. and 300 ° C., under a pressure of between 1 and 3 MPa, at a liquid hourly space velocity   between 1 h-4 and 10 h-4 and with a ratio H2 / HC of between 50 I / l and 500 I / l.   7. Method according to one of the preceding claims wherein the rate of   Desulfurization of the second desulfurization is strictly greater than 80%.   8. Method according to one of the preceding claims wherein the difference between   the desulfurization rates of the first and second desulfurization are from to   minus one percent in absolute value.   9. Method according to one of the preceding claims further comprising a   additional step of selective hydrogenation of the diolefins contained in the   section, said step being performed before the first desulphurization.   10. Method according to one of the preceding claims further comprising a   additional step of increasing the weight of light sulfur compounds, said step   being performed before the first desulfurization.   11. Method according to one of the preceding claims further comprising at least   an additional step of separating said cut into at least two fractions including: a light fraction containing a minor portion of the sulfur compounds, a heavy fraction containing the majority of the sulfur compounds, at least said heavy fraction being then treated according to the first desulfurization step.   12.Application of the method according to one of the preceding claims to essences   from catalytic cracking or coking of a heavy load