EP0333554A1 - Thermal-treatment process of hydrocarbon feeds in the presence of polysulfides and hydrogen donors - Google Patents

Abstract

Process for heat treatment of hydrocarbon feedstocks carried out in the presence of hydrogen polysulphides, aliphatic polysulphides and/or alicyclic polysulphides and of at least one hydrogen-donating compound in an inert atmosphere, for example under argon or in the presence of a gas containing hydrogen. The quantity of polysulphide is usually from 0.01 to 1 gram-atom of sulphide per 100 grams of feedstock to be treated and the quantity of hydrogen donor introduced is usually from 10 to 400 % by weight relative to the feedstock to be treated. <IMAGE>

Description

Description PROCESS FOR THE HEAT TREATMENT OF HYDROCARBON CHARGES IN THE PRESENCE OF POLYSULFIDES AND HYDROGEN DONORS

The present invention relates to a process for heat treatment of hydrocarbon feedstocks and more particularly heavy feedstocks in the presence of hydrogen polysulfides and / or organic polysulfides and hydrogen donors. It is particularly applicable to the petroleum refining industry and in particular to thermal conversion processes such as visbreaking and non-catalytic hydroviscoreduction, that is to say without adding metals or metal compounds having a catalytic action on the reactions which occur. during heat treatment of the load.

In other words, the present invention applies to methods of heat treatment of hydrocarbon charges in which the overall H / C ratio of the recipe (of effluents) is not significantly different from that of the charge to be treated .

Improvement of heat treatment processes used in the petroleum industry, in particular for the refining of fossil organic materials rich in high-mass polyaromatic structures, coke promoters, such as heavy and related oils: bituminous shales, asphalt sands, etc. and the refining residues, implies a control of the radical transformation processes by the use of efficient solvents or additives.

Numerous studies have been devoted to the use of hydrogen-donating solvents (hydropolyaromatic structures such as tetralin, dihydroanthracene or partially hydrogenated petroleum fractions), capable of effectively inhibiting the development of radical polycondensation or polymerization reactions. chain (US-A-2796386, US-A-4425224).

However, under identical conditions, the use of an efficient hydrogen donor leads to a more moderate conversion into light fractions when reactive intermediates which promote chain fragmentation processes are eliminated from the reaction medium. This aspect of the problem has led to the association of additives capable of carrying out together the radical capture and the activation of the fragments of the polymolecular aggregates present in these heavy fractions.

Various studies mention the effect of hydrogen sulfide, present during the treatment of sulfur-rich petroleum fractions, as a compound capable of a double catalytic role: on the one hand, the improvement of the kinetics of hydrogen transfer therefore of the efficiency of free radical capture; on the other hand, the activation of fragmentation reactions.

French patent FR-B-2555192 describes in particular the use of nickel naphthenate as an anti-coke additive optionally combined with dimethyldisulfide (DMDS). This process makes it possible to reduce, at isoconversion, the amount of insoluble matter in xylene (coke). It is noted however that on the one hand there is still a significant amount of coke and that on the other hand the conversion is greatly reduced compared to a heat treatment carried out without additive. It is noted, moreover, on reading the Table of this document, that the additional addition of DMDS to nickel naphthenate does not make it possible to improve the conversion (yield at 350 ° C.) or to reduce the amount of coke formed (insoluble in xylene) significantly. The addition of metal compounds, to the load, usually imposes the need for a subsequent treatment of the effluent obtained after the heat treatment in order to separate and possibly recycle these compounds, which can be a major handicap for the process.

It is also known from patent EP-A-0.175.511 to use a sulfur-containing compound such as thiophenol in the presence of a hydrogen-donor diluent, the latter having to be combined with compounds having properties approaching those of aromatic hydrocarbons (thiophenol for example). In addition, thiophenol is an expensive compound which would put a strain on the economy of its method of use.

• - le domaine thermique de formation des espèces réactives est trop limité à partir de générateurs tels que l'eau oxygénée, les hydroperoxydes et les peroxydes organiques. Cette température, inférieure en général à 200 °C, conduit à une stabilité insuffisante pour leur action efficace dans le milieu aux températures habituellement en vigueur.
• - leur action consiste plutôt en une modification chimique préalable au traitement thermique proprement dit ; de plus, une mauvaise sélectivité est observée du fait de la décomposition souvent brutale et exothermique de ces composés.

Other types of activators have been recommended in the prior art, such as radical generators; in general, these additives have various reaction shortcomings, in particular:

• - the thermal domain of formation of reactive species is too limited from generators such as hydrogen peroxide, hydroperoxides and organic peroxides. This temperature, generally lower than 200 ° C., leads to insufficient stability for their effective action in the medium at the temperatures usually in force.
• - their action rather consists of a chemical modification prior to the actual heat treatment; in addition, poor selectivity is observed due to the often brutal and exothermic decomposition of these compounds.

The object of the invention is in particular to remedy the drawbacks indicated above.

It has been discovered, surprisingly, that a non-catalytic heat treatment of a hydrocarbon feed can be obtained, a high conversion into lighter, liquid fractions which are easily recoverable (for example into industrial fuels). and simultaneously a clear reduction in the formation of coke, while remaining in the usual temperature range for such treatments.

The synergy observed during the concomitant use of hydrogen donors and hydrogen polysulfides and / or organic polysulfides also makes it possible to carry out heat treatments which convert at higher temperatures and thus to obtain a higher conversion into effectively limiting the formation of coke and gases. It also makes it possible advantageously to avoid in certain cases the use of molecular hydrogen in visbreaking processes.

In general, the invention relates to a process for the thermal conversion of a hydrocarbon feedstock, for example a heavy petroleum cut, a refining residue, or a heavy petroleum in which said feedstock is subjected to a heat treatment, said process being characterized in that the heat treatment is carried out in the presence of at least one polysulfide chosen from the group formed by hydrogen polysulfides and organic polysulfides and at least one hydrogen donor compound . The polysulfide used in the present invention is usually a compound of formula (I) R ^{1 -} (S) _n - R ² in which R ¹ and R ² , identical or different, each represent a hydrogen atom or a hydrocarbon radical and n is a number between 2 and 20, limits included and preferably between 2 and 8, limits included.

Mention may be made, among hydrocarbon radicals, by way of example, of saturated or unsaturated, linear or branched aliphatic radicals, cycloaliphatic radicals and aryl radicals. In formula (I) above, R ¹ and R ² independently of one another represent a hydrogen atom, a linear or branched alkyl radical, an aryl radical, an aryl-alkyl (aralkyl) radical or a cycloalkyl radical.

Advantageously, polysulphides of formula (I) are used in which at least one of the radicals R ¹ and R ² represents a hydrocarbon radical and preferably those in which R ¹ and R ² , identical or different, each represent a saturated aliphatic radical or unsaturated, linear or branched or an alicyclic radical. The particularly preferred organic polysulphides of formula (I) are those in which R ¹ and R ² , which are identical or different, each represent an alkyl radical; they are hereinafter called dialkyl-polysulfides. By way of example of organic polysulphides, mention may be made of aliphatic and / or alicyclic disulphides and more particularly dialkyl disulphides.

The organic polysulfides of formula (I) used in the present invention usually have from 2 to 72 carbon atoms and preferably from 2 to 48 carbon atoms in their molecule.

The dialkylpolysulfides used advantageously have from 2 to 24 carbon atoms in their molecule and the organic polysulfides of formula (I) in which R ¹ and / or R ² represent an aryl, aralkyl or cycloalkyl radical advantageously have from 6 to 48 carbon atoms and preferably from 10 to 32 carbon atoms in their molecule.

By way of specific examples of organic polysulfides, mention may be made of dimethyldisulfide (DMDS), diethyldisulfide (DEDS), dipropyldisulfides, dibutyldisulfides, in particular ditertiobutyldisulfide (DTBDS), ditertiobutylpolysulfide (n = 5) and ditertod n = 5) marketed for example by ELF AQUITAINE under the name TPS 32, in particular because it contains approximately 32% by weight of sulfur and the ditertiononylpolysulfide (n = 5) marketed for example by ELF AQUITAINE under the name TPS 37.

The hydrocarbon polysulphides can result, in a particularly advantageous manner, from the oxidation, under conditions known per se, of the mercaptans contained in LPG petroleum fractions and advantageously light essences, (attractive Merox process). These cuts, once oxidized, can be made to the load to be visbreaked.

The amount of polysulphide used in the present invention, expressed in gram atom of sulfur per 100 g of load to be treated is usually from 0.01 to 1 gram atom of sulfur, preferably from 0.05 to 0.5 atom -gram of sulfur and most often from 0.08 to 0.3 gram-atom of sulfur, which corresponds by weight of sulfur relative to the load at: 0.32% to 32%, preferably 1.6 ⁰ / o at 16% and most often 2.56% at 9.6%.

By way of example of hydrogen-donating compounds, mention may be made of the at least partially hydrogenated derivatives of naphthalene, anthracene, pyrene, fluoranthene, benzoanthracene, dibenzoanthracene, coronene, perylene, benzopyrene, their nitrogen heterocyclic analogs and their analogs substituted by at least one lower alkyl radical having for example from 1 to 10 carbon atoms. Mention may also be made, for example, of LCO (Light Cycle Oil) or HCO (Heavy Cycle Oil) cuts such as 180 - 365 ° C or 320 - 500 ° C cuts, for example from catalytic cracking, LCO cuts or HCO at least partially hydrogenated, and polyaromatic cuts possibly at least partially hydrogenated; the hydrocarbon fractions used as hydrogen donor are usually those which contain at least 0.8% by weight and preferably at least 1.25% by weight of transferable (or transferable) hydrogen such as for example those mentioned in the patent US-A-4425224.

As specific examples of hydrogen donor compounds, mention may be made of tetrahydronaphthalene or tetralin (TN), dihydroanthracenes, tetrahydroanthracenes, dihydrobenzoanthracenes and dihydrodibenzoanthracenes. The amount of hydrogen donor used is usually from 10 to 400% by weight, preferably from 30 to 200% by weight and most often from 40 to 150% by weight relative to the weight of the feed to be treated.

The synergistic effect of the action of the polysulphide and of the hydrogen donor is particularly important when the quantity of polysulphide used expressed in weight percent of sulfur relative to the charge to be treated is from 2.56 to 9.6 % and that the amount of hydrogen donor is 30 to 200% by weight and more particularly 40 to 150% by weight relative to the charge to be treated.

The invention applies to various thermal treatments of hydrocarbon feedstocks usually having a viscosity of between approximately 600 and 70,000 mPa x s at 100 ° C and most often between approximately 1000 and 30,000 mPaxs at 100 ° C. The invention applies in particular to visbreaking and hydroviscoreduction of distillation residues, for example residues of vacuum distillation (RSV) or atmospheric distillation.

The visbreaking is usually carried out at temperatures of about 350 to 500 ° C, preferably about 380 to 450 ° C and most often about 410 to 450 ° C and the hydroviscoreduction at temperatures of the same order of greatness.

The total pressure is usually about 1 MPa to 20 MPa at processing temperatures and the residence time is usually about 1 minute to 3 hours.

In the case of visbreaking, the heat treatment is usually carried out under an inert atmosphere, for example under argon, helium or nitrogen or under an atmosphere of water vapor or of a mixture of water vapor and inert gas.

In the case of hydroviscoreduction, the heat treatment is carried out in the presence of hydrogen, preferably substantially pure, or a mixture of substantially pure hydrogen and inert gas, although it is also possible to use industrial hydrogen containing for example less than about 5% by volume of hydrogen sulfide and preferably less than about 2.5% by volume of hydrogen sulfide. The invention also relates to a composition for carrying out the process according to the present invention, comprising on the one hand at least one polysulfide as defined above and on the other hand at least one hydrogen donor compound.

The weight ratio of the hydrogen donor to the polysulfide in said composition is usually about 0.3 1 to 1250: 1, preferably about 1.87: 1 to 125: 1 and most often about 4.2: 1 to 58.6: 1.

The proportion by weight of the composition introduced into the filler to be subjected to the heat treatment is usually about 10.3 to 432 parts per 100 parts of the filler to be treated, consisting, for example, of a heavy fraction of petroleum, preferably of about 31.6 to 216 parts per 100 parts of said load and most often about 42.6 to 159.6 parts per 100 parts of said load.

The following examples illustrate the invention and should in no way be taken as limiting.

EXAMPLES 1 to 16

Examples 1, 2, 3, 5, 7, 9, 10, 11, 13 and 15 are given for comparison and do not form part of the invention.

Examples 1 to 16 were carried out batchwise. Examples 1 to 8 relate to visbreaking, of a residue under vacuum, carried out under argon and Examples 9 to 16 relate to hydroviscoreduction, carried out in the presence of substantially pure hydrogen, of the same charge.

The hydrocarbon feedstock used in the examples is a vacuum residue (RSV) 500 ° C ⁺ of SAFANIYA origin, the characteristics of which are given in Table 1 below.

• - on chauffe l'échantillon sous atmosphère inerte jusqu'à une température T1, puis après un palier à la température T1, on chauffe l'échantillon jusqu'à une température T2 que l'on maintient un certain temps. On réalise une combustion des effluents de chauffage par un mélange de gaz (Hélium + 3 % d'oxygène en volume (He + 3 % 0₂)) en présence d'un catalyseur d'oxydation (CuO) ; les composés d'oxydation, notamment C0₂, sont détectés par exemple par un détecteur à infrarouge ; et
• - le résidu restant après chauffage en atmosphère inerte est à son tour oxydé avec le même mélange (He + 3 % 0₂) jusqu'à une température T3 et, après passage sur un catalyseur CuO, les composés d'oxydation du résidu (carbone résiduel) sont détectés par le même type de détecteur et les signaux traités par un calculateur.

The untreated vacuum residue and the liquid fraction resulting from visbreaking or hydroviscoreduction were analyzed by pyroanalysis. This method includes the following steps:

• the sample is heated under an inert atmosphere to a temperature T1, then after a plateau at the temperature T1, the sample is heated to a temperature T2 which is maintained for a certain time. Combustion of the heating effluents is carried out with a mixture of gases (helium + 3% oxygen by volume (He + 3% 0 ₂ )) in the presence of an oxidation catalyst (CuO); the oxidation compounds, in particular C0 ₂ , are detected for example by an infrared detector; and
• - the residue remaining after heating in an inert atmosphere is in turn oxidized with the same mixture (He + 3% 0 ₂ ) up to a temperature T3 and, after passage through a CuO catalyst, the oxidation compounds of the residue (carbon residual) are detected by the same type of detector and the signals processed by a computer.

• VA = VC = 20 °C/minute ; VE = 150 °C/minute
• tA = 11 minutes, tB = 10 minutes, tC = 14 minutes, tD = 10 minutes,
• tE = 2 minutes et tF = 10 minutes.

The heating temperature profile illustrated in Figure 1 is as follows:

• VA = VC = 20 ° C / minute; VE = 150 ° C / minute
• tA = 11 minutes, tB = 10 minutes, tC = 14 minutes, tD = 10 minutes,
• tE = 2 minutes and tF = 10 minutes.

The point P1 corresponds to the standard n-alkane heated under the same conditions and the boiling point of which is approximately 500 ° C. From the point P2 the combustion rich in carbon is carried out. A calibration is also carried out using crude oil, the simulated distillation of which is known.

The pyrogram obtained (Figure 2) delivers the C0 ₂ concentration as a function of the time and temperature of the oven. It is thus easy to split the pyrogram by integration of the signal between temperature values chosen for example according to the fractions below. In the case of the untreated vacuum residue, the percentages of the various fractions are indicated below:

The fraction F2 represents the fraction 500 ° C at the end
distillation (FD).

By calibrating the response of the detector it is easy to obtain the carbon weights corresponding to the above fractions. Similarly, the percentages and weights of hydrogen and sulfur contained in the sample are obtained simultaneously with those of carbon.

The centesimal analysis of the charges subjected to hydroviscoreduction shows that the sum of the weights of C, H and S is always greater than or equal to 95 o / o. Consequently, the simple addition of these weights makes it possible to obtain with sufficient precision the actual respective percentages of the various above fractions of the liquid fraction.

This analysis method is used for all examples 1 to 16.

The concentrations by weight of polysulphides are such that the level of sulfur introduced with respect to the charge to be treated is equal to 0.2 gram atom of sulfur per 100 g of RSV SAFANIYA in examples 3 to 6, 8, 11 to 14 and 16.

The petroleum charge (RSV SAFANIYA) after slight heating (100 -120 ° C) to make it less viscous, is introduced into the reactor which is a stainless steel autoclave in the case of examples 1 to 16. The whole is constantly restless. Any additives are added after cooling.

All of the examples 1 to 16 of visbreaking and visbreaking were carried out under an initial pressure (at 20 ° C.) of 5 MPa, at high severity, at 430 ° C. for 15 minutes, after a time for the temperature to rise. heat treatment of approximately 25 minutes.

The concentrations chosen by way of example as a hydrogen donor diluent (DDH) are such that the weight ratio RSV / DDH is equal to 1.

In the presence of DDH and polysulphide simultaneously, the weight concentrations of each of its additives with respect to RSV are identical to those used with the additives alone.

• - une phase solide, le coke,
• - une phase liquide contenant une partie des produits initiaux ou des produits de craquage, et
• - une phase gazeuse.

After the visbreaking or hydroviscoreduction treatment, we generally obtain a system likely to be multiphase:

• - a solid phase, coke,
• a liquid phase containing part of the initial products or of the cracking products, and
• - a gas phase.

The liquid products and any coke are collected directly or by dissolution in benzene, this operation being followed by evaporation; the gases are not recovered but are calculated by difference between the quantities introduced and collected.

Coke is defined as the part insoluble in hot benzene. An assay is carried out for each test. The amount of liquid is calculated after determining the coke level.

The levels of gas, liquid and coke are expressed relative to petroleum alone or relative to the petroleum + DDH mixture, after deduction of the polysulphurized additives where appropriate. It is therefore implicitly assumed that the additive, even if it undergoes significant modifications during pyrolysis, can be recovered mainly in the liquid fraction (case for example of tetralin, LCO and diphenyldisulfide) or in the gas phase (case dimethyldisulfide).

As an example, the calculation of the overall conversion is detailed below in the case of Example 12. This calculation takes into account the complete conversion of the DMDS into a gaseous fraction (H ₂ S + CH ₄ ) deductible from the weight. of the total gas fraction obtained after the hydroviscoreduction treatment.

The charge subjected to the hydroviscoreduction comprises 47.6 g of RSV SAFANIYA, 47.6 g of tetralin and 4.8 g of DMDS, ie 100 g of raw material subjected to the heat treatment.

After treatment, 0.7 g of coke (insoluble in benzene from the liquid fraction) and 94.2 g of overall liquid fraction are isolated. By difference at 100 g, the weight of the overall gas fraction is deducted, ie 5.1 g. The gas is composed of H ₂ S and CH ₄ from the DMDS, ie 4.8 g, therefore the weight of the gaseous fraction formed from the RSV is 0.3 g.

The petroleum liquid fraction consists of tetralin and effluents from the hydroviscoreduction of RSV which therefore represent 94.2 - 47.6 = 46.6 g.

The conversion (Y), given in the tables below, is calculated using the following formula:

The recipe consists of all of the products from visbreaking or hydroviscoreduction (gas + liquid + solid (coke)).

The 500 ° C ⁺ percentage (% 500 ° C ⁺ ) of the recipe therefore contains the 500 ° C ⁺ liquid fraction of the liquid part of the recipe and possibly the coke formed during the heat treatment.

The percentage 500 ° C- (% 500 ° C-) of the recipe contains the gases formed and the fraction 500 ° C- liquid of the liquid part of the recipe.

If we designate by G, L and C respectively the percentage of gas, liquid and coke of the recipe (G + L + C = 100% of the recipe) the conversion Y is then expressed by the following formula:

The analysis of the liquid part of the recipe is carried out by pyroanalysis as explained above. To perform the calculations, it is therefore a question of converting the various weight percentages into percentages of carbon. The difference between the usual weight and the carbon weight is small when the additive introduced contains a high proportion of carbon (case of tetralin: carbon content: 90.91%) but it is no longer so when introduces an additive such as for example dimethyldisulfide (DMDS: carbon content 25.0%) or diphenyldisulfide (DPDS: carbon content 66%)

• RSV = 47,6 % x 83,27 % = 39,64
• Tétraline (TN) = 47, 6 % x 90,91 % = 43,27
• soit une répartition en % poids de carbone pour la charge de :
• RSV = 39,64/(39,64 + 43,27) = 47,8%
• TN = 43,27/(39,64 + 43,27) = 52,2%.

The carbon composition of the starting charge is thus calculated by deducting the polysulphide introduced (case of Example 12: DMDS):

• RSV = 47.6% x 83.27% = 39.64
• Tetralin (TN) = 47.6% x 90.91% = 43.27
• or a distribution in% weight of carbon for the charge of:
• RSV = 39.64 / (39.64 + 43.27) = 47.8%
• TN = 43.27 / (39.64 + 43.27) = 52.2%.

• 500 °C- : 6%
• 500 °C⁺ distillable (FD) : 78 %
• Carbone résiduel (R) = 16%.

The distribution in fractions 500 ° C-, 500 ° C ⁺ distillable, and residual carbon of the untreated RSV, analyzed by pyroanalysis and expressed in% weight of carbon is:

• 500 ° C-: 6%
• 500 ° C ⁺ distillable (FD): 78%
• Residual carbon (R) = 16%.

• 500 °C = 52,2 + 47,8 x 6 % = 55,1 %
• 500 °C⁺ (FD) = 47,8 x 78 % = 37,3%
• R = 47,8 x 16 = 7,6%.

The distribution of the charge in% weight of carbon in the case of Example 12 is therefore:

• 500 ° C = 52.2 + 47.8 x 6% = 55.1%
• 500 ° C ⁺ (FD) = 47.8 x 78% = 37.3%
• R = 47.8 x 16 = 7.6%.

The analysis of the recipe, in the case of Example 12, by pyroanalysis provides, deducing the DMDS, the following results:

• 500 ° C- = 78,8 %
• 500 °C⁺ (FD) = 15,1 %
• Carbone résiduel (R) = 6,1 %.

The analysis of the liquid part of the recipe, whose fractions represent 100% by pyroanalysis, gives the following results:

• 500 ° C- = 78.8%
• 500 ° C ⁺ (FD) = 15.1%
• Residual carbon (R) = 6.1%.

Y = 51,7%The conversion (Y) of the 500 ° C ⁺ fraction of the feed, in the case of Example 12, into the 500 ° C- fraction is therefore:

Y = 51.7%

Table 2 summarizes the results of Examples 1 to 8 carried out under an initial argon pressure of 5 MPa at 430 ° C (visbreaking).

Table 3 summarizes the results of Examples 9 to 16 carried out under an initial hydrogen pressure of 5 MPa at 430 ° C (water reduction).

Table 4 gives the characteristics of a non-hydrogenated LCO originating from the catalytic cracking used as hydrogen donor in Examples 7, 8, 15 and 16.

Table 5 compares at a low conversion temperature the action of thiophenol and the action of dimethyldisulfide in the presence of hydrogen donor.

It is noted on reading the results presented in Tables 2 and 3 that the combination of an organic polysulphide DMDS or DPDS and a hydrogen donor (TN or LCO) makes it possible to obtain (examples 4, 6, 8 , 12, 14 and 16) quantities of coke very close to or even lower than those obtained with tetralin as the only additive (examples 2 and 10) but with a much higher conversion (13 and 18 points more, respectively in the example 2 compared to example 4 and example compared to example 12). Examples 12 A and 12 B show that the ditertiobutylpentasulfide gives in combination with tetralin a result substantially similar to that of Example 12, with a few points of conversion.

Examples 12 C and 12 D are given for comparison and show that Example 12 according to the invention gives better results than Example 12 D according to the prior art in the presence of dimethyldisulfide alone and molybdenum naphthenate as catalyst. .

These results clearly show the advantage of the association of a hydrogen donor and an organic polysulfide which allows during the thermal conversion to keep the advantage obtained by adding the hydrogen donor to the charge (formation of reduced coke, see examples 2 and 10, while retaining most of the advantage obtained by adding polysulphide (high conversion) without having the disadvantage (very high coke formation, see examples 3, 5, 11 and 13 ).

In the case of the use of an LCO, not previously hydrogenated, it is noted that the use in combination of this LCO and an organic polysulfide (examples 8 and 16) makes it possible to obtain a higher conversion than during using the same LCO alone (examples 7 and 15). This simultaneous use does not lead to an excessive increase in the formation of coke that might have been expected due to the use of an organic polysulfide (see examples 3 and 11).

EXAMPLES 17 to 21

Examples 17 to 21 illustrate a conversion carried out on the same Safaniya residue under initial 5 MPa hydrogen pressure at 390 ° C. for 15 minutes. A comparative study is carried out between thiophenol (prior art), dimethyldisulfide and ditertiobutylpentasulfide (X) in the presence of tetrahydronaphthalene (TN) and presented in Table 5 where the symbols are the same as those used in the previous tables. The tetralin-polysulfide association according to the invention gives better results.

EXAMPLES 22 to 25

• Température : 450 °C
• Temps de séjour de la charge : 1 heure
• Débit d'hydrogène : 1,1 1/minute à température et pression normales
• Débit de charge liquide : 5 ml/minute.

Examples 22 to 25 were carried out in a micropilot, under a pressure of 10 MPa of substantially pure hydrogen, continuously, under the following conditions:

• Temperature: 450 ° C
• Charge residence time: 1 hour
• Hydrogen flow: 1.1 1 / minute at normal temperature and pressure
• Liquid charge flow: 5 ml / minute.

The charge used is the same as that used in Examples 1 to 21. The analysis method used in Examples 22 to 25 is the same as that used in Examples 1 to 21.

The concentrations by weight of polysulphides are such that the level of sulfur introduced with respect to the charge to be treated is equal to 0.2 gram-atom of sulfur per 100 g of RSV SAFANIYA in Example 19 and to 0.1 atom- gram of sulfur in Examples 23 and 25.

The results obtained are presented in Table 6 below, they confirm the results obtained in batch in Examples 1 to 21 and show the advantage obtained by the association of polysulfide and hydrogen donor allowing the reduction of the formation. coke while greatly increasing the conversion compared to the case of using a hydrogen donor alone.

Claims (15)

1 - Process for the thermal conversion of a hydrocarbon feedstock, characterized in that said feedstock is subjected to a heat treatment in the presence of at least one polysulfide chosen from the group formed by hydrogen polysulfides, aliphatic polysulfides and alicyclic polysulfides and at least one hydrogen donor. 2 - Process according to claim 1 in which the polysulfide is a compound of formula (I) R ^{1 -} (S) _n - R ² in which R ¹ and R ² identical or different, each represent a hydrogen atom, or a saturated or unsaturated, linear or branched aliphatic hydrocarbon radical or an alicyclic hydrocarbon radical and n is a number between 2 and 20, limits included. 3 - Process according to claim 1 or 2 wherein the polysulfide comprises from 2 to 72 carbon atoms in its molecule. 4 - Method according to one of claims 1 to 3 wherein the polysulfide is an aliphatic and / or alicyclic disulfide. 5 - Method according to one of claims 1 to 4 wherein the polysulfide is a dialkyldisulfide having 2 to 48 carbon atoms in its molecule. 6 - Method according to one of claims 1 to 4 wherein the polysulfide is selected from the group formed by dimethyldisulfide, diethyldisulfide, dipropyldisulfides, dibutyldisulfides, ditertiododecylpolysulfide (n = 5), ditertiononylpolysulfide (n = 5) and ditertiobutylpolysulfide (n = 5). 7 - Method according to one of claims 1 to 6 wherein the polysulfides result from the oxidation of the mercaptans contained in petroleum LPG and petroleum fractions. 8 - Method according to one of claims 1 to 7 wherein the amount of polysulfide involved is from 0.32% to 32% by weight of sulfur relative to the feed to be treated. 9 - Method according to one of claims 1 to 8 wherein the hydrogen donor is selected from the group formed by at least partially hydrogenated derivatives of naphthalene, anthracene, pyrene, fluoranthene, benzoanthracene, dibenzoanthracene, coronene, perylene, benzopyrene, their heterocyclic analog derivatives, their analog derivatives substituted by at least one lower alkyl radical, the LCO and / or HCO cuts, the LCO and / or HCO cuts at least partially hydrogenated, polyaromatic cuts and polyaromatic cuts at least partially hydrogenated. 10 - Method according to one of claims 1 to 9 wherein the hydrogen donor is selected from the group formed by tetrahydronaphthalene, dihydroanthracenes, tetrahydroanthracenes, dihydrobenzoanthracenes, dihydrodibenzoanthracenes and an LCO cut (180 - 365 ° C ). 11 - Method according to one of claims 1 to 10 wherein the amount of hydrogen donor involved is 10 to 400% by weight relative to the charge to be treated. 12 - Method according to one of claims 1 to 11 characterized in that said heat treatment consists of a visbreaking or a hydroviscoreduction. 13 - Composition usable for implementing the method according to one of claims 1 to 12 characterized in that it comprises on the one hand at least one polysulfide chosen from the group formed by hydrogen polysulfides and hydrocarbon polysulfides aliphatic or alicyclic and on the other hand at least one hydrogen donor compound. 14 - Composition according to claim 13 wherein the polysulfide is a dialkyldisulfide having from 2 to 48 carbon atoms in its molecule and the hydrogen donor compound is chosen from the group formed by at least partially hydrogenated derivatives of naphthalene, l anthracene, pyrene, fluoranthene, benzoanthracene, dibenzoanthracene, coronene, perylene, benzopyrene, their heterocyclic analog derivatives, their analog derivatives substituted by at least one lower alkyl radical, the LCO and / or HCO cuts , LCO and / or HCO cuts at least partially hydrogenated, polyaromatic cuts and polyaromatic cuts at least partially hydrogenated. 15 - Composition according to claim 13 or 14 wherein the weight ratio of the hydrogen donor compound to the polysulfide is from about 0.3: 1 to 1250: 1.

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