IMPROVED PROCESS FOR THE DEHYDROGENATION OF HYDROCARBONS

Abstract

The present invention relates to a process for dehydrogenating a hydrocarbon chain, in at least one reactor in the presence of a catalyst; said process comprising a step of introducing a metal M upstream or at the inlet of the reactor(s), and said metal M being chosen from the group consisting of zinc (Zn), tin (Sn), indium (In), zirconium (Zr), cerium (Ce), germanium (Ge), gallium (Ga), lead (Pb) and thallium (Tl), preferably zinc. Figure: None

Description

Title of the invention: IMPROVED PROCESS FOR THE DEHYDROGENATION OF HYDROCARBONS

[0001] The present invention relates to an improved process for the dehydrogenation of hydrocarbon chains (or hydrocarbons). The present invention also relates to a composition allowing in particular the implementation of such a process.

[0002] The dehydrogenation of hydrocarbon chains, and in particular alkanes, is of great industrial interest. Indeed, there is a growing demand for dehydrogenated hydrocarbon chains (hereinafter called alkenes or olefins), which are essential synthesis intermediates for the chemical industry.

[0003] Thus, the transformation of propane into propylene and isobutane into isobutene is of particular interest to manufacturers. Propylene is mainly polymerized into polypropylene (PP), a consumer polymer. It is used, for example, in the manufacture of molded parts in the automotive sector, food packaging, upholstery fabrics, disposable professional clothing, or as an additive to concrete. Isobutene can be used to produce methyl tert-butyl ether or be polymerized into polyisobutene (PIB). This polymer is used for the manufacture of inner tubes or inner linings for tubeless tires. Its secondary applications are very varied: manufacture of chewing gum, sealants and vibration damping, adhesives, coatings, cosmetic products, insulating oils, and others.

[0004] Catalytic dehydrogenation of hydrocarbon chains has been known for a long time. However, to date, the yields of these catalytic processes are between 50% and 85%. In view of the growing demand for olefins, it is desirable to improve these yields.

[0005] There is therefore a need to improve existing dehydrogenation processes and in particular to improve their efficiency. There is a need for more efficient, more economical and easy to implement dehydrogenation processes.

[0006] The present invention aims to provide an improved process for dehydrogenating hydrocarbon chains, preferably with an improved yield.

[0007] The present invention also aims to provide an improved dehydrogenation process which is easy to implement, and in particular which does not involve any modification of pre-existing industrial installations.

[0008] The objective of the present invention is to provide a composition that is easy to use by process operators, making it possible to improve the dehydrogenation reaction while being compatible with industrial installations.

[0009] The invention meets all or part of the above objectives.

[0010] The present inventors have discovered that the introduction upstream or at the inlet of the dehydrogenation reactor of at least one metal M as defined below, improves the yield of the reaction and / or increases the lifetime of the catalyst. In particular, the introduction of the metal M according to the invention makes it possible to obtain an increase in yield of between 1% and 10%, preferably between 2% and 5%. The addition of the metal M can allow a controlled improvement in the yield, in particular thanks to a specific and adapted formulation of said metal M.

[0011] Without wishing to be bound by theory, the introduction of metal M makes it possible to generate more active catalytic sites on the dehydrogenation catalyst. In addition, when the catalyst comprises several metals, the organization of the metal catalytic sites may prove difficult to control. Also, the addition of metal M according to the invention makes it possible to improve and / or control the activity of the catalyst. The invention may also allow the use and handling of less complex and less toxic catalysts, which will possibly be easier to regenerate.

[0012] Adding a metal M separate from the catalyst, and possibly continuously, also makes it possible to combat its progressive deactivation, a problem well known to manufacturers in this type of process.

[0013] The inventors have also discovered that in the form of an organometallic compound as defined below, said metal M improves the yield of the reaction while being perfectly suited to the process and the installations in which it is implemented. Indeed, the organometallic compounds according to the invention can be solubilized in all or part of the reagent (i.e. in the hydrocarbon chain to be dehydrogenated) and / or be solubilized in other additives introduced into the process.

[0014] In a particularly preferred and surprising manner, these organometallic compounds can be solubilized in compositions limiting or preventing the formation of coke (in particular on the catalyst), while maintaining the efficiency gain. Such compositions generally comprise sulfur compounds which will make it possible to passivate the metallurgy of the reactor and / or selectively poison the catalyst to limit or prevent the formation of coke.

[0015] Thus, the organometallic compounds such as according to the invention can be solubilized in compositions comprising sulfur compounds as defined below. Alternatively, one can speak of a sulfur compound with an organometallic compound added. For example, one speaks of dimethyl disulfide (hereinafter called DMDS) with an organometallic compound added.

[0016] These compositions have the advantage of being able to be introduced into the process at the point(s) of introduction of additive(s) already in place in the dehydrogenation unit and allow controlled dosing of the quantity of metal M introduced. Thus, No modifications to the installations are necessary to improve the dehydrogenation process, which is a great advantage for manufacturers. BRIEF DESCRIPTION OF THE INVENTION

[0017] It is specified that the expressions “from ... to ...” and “between ... and ...” used in the present description must be understood as including each of the limits mentioned.

[0018] It is also specified that the ppm express a mass fraction, unless expressly stated otherwise.

[0019] The present invention relates to a process for preparing an olefin, which may also be called a dehydrogenation process. Said process comprises a step of dehydrogenation of a hydrocarbon chain (called step b) below), in at least one reactor in the presence of a catalyst;

[0020] said method comprising a step of introducing (called step a) hereinafter) a metal M upstream or at the inlet of the reactor(s), and

[0021] said metal M being chosen from the group consisting of zinc (Zn), tin (Sn), indium (In), zirconium (Zr), cerium (Ce), germanium (Ge), gallium (Ga), lead (Pb) and thallium (Tl), preferably zinc.

[0022] The present invention also relates to a composition comprising: a sulfur compound of the following general formula (I):

[0023] [Chem.l] IM (I)

[0024] in which:

[0025] - R is chosen from a linear or branched alkyl radical, containing from 1 to 4 atoms of carbon and a linear or branched alkenyl radical, containing from 2 to 4 carbon atoms,

[0026] - n is an integer equal to 0, 1 or 2,

[0027] - x is an integer chosen from 0, 1, 2, 3 or 4, and

[0028] - R' is chosen from a linear or branched alkyl radical, containing from 1 to 4 atoms of carbon; a linear or branched alkenyl radical, containing from 2 to 4 carbon atoms, and only when n=x=0, a hydrogen atom; and a metal M selected from the group consisting of zinc (Zn), tin (Sn), indium (In), zirconium (Zr), cerium (Ce), germanium (Ge), gallium (Ga), lead (Pb) and thallium (Tl), preferably zinc.

[0029] The present invention also relates to the use of said metal M in a process for dehydrogenation of a hydrocarbon chain, preferably for increase yield.

[0030] The present invention also relates to the use of said composition in a process for dehydrogenating a hydrocarbon chain, preferably to increase the yield thereof.

[0031] Preferably, said metal M is in the form of an organometallic compound of general formula (II) as defined below. DETAILED DESCRIPTION OF THE INVENTION

[0032] The dehydrogenation reaction of hydrocarbon chains is a widely known reaction (see WO 2020 / 081421 and EP 3 240 770 for example). This reaction makes it possible to form a C=C double bond and in particular to obtain mono-olefins from alkanes and / or diolefins from mono-olefins. Preferably, alkanes are used to obtain mono-olefins.

[0033] By "hydrocarbon chain" is meant in particular an alkane or an olefin. It can have between 2 and 30 carbon atoms, preferably between 2 and 10 carbon atoms.

[0034] By “alkane” is meant in particular a saturated, linear, branched or cyclic hydrocarbon chain, preferably linear.

[0035] By “olefin” is meant in particular an unsaturated hydrocarbon chain, which may be a mono- or di-olefin, linear, branched or cyclic, preferably linear.

[0036] By "mono-olefin" is meant an unsaturated hydrocarbon chain comprising a single C=C double bond. By "diolefin" is meant an unsaturated hydrocarbon chain comprising two C=C double bonds.

[0037] The alkanes to be dehydrogenated may contain between 2 and 30 carbon atoms, for example between 2 and 10 carbon atoms, preferably between 3 and 6 carbon atoms. Propane, butane, isobutane and mixtures thereof are preferred, and most preferably propane, isobutane and mixtures thereof.

[0038] The monoolefins to be dehydrogenated may contain between 3 and 30 carbon atoms, for example between 3 and 10 carbon atoms, preferably between 3 and 6 carbon atoms. Mention may be made of but-1-ene.

[0039] Said hydrocarbon chains may be in liquid, gaseous form or in a gas-liquid mixture. They may be introduced as a mixture with a diluent into the dehydrogenation reactor. Said mixing with the diluent may be carried out upstream, at the inlet or in the reactor. Examples of diluents that may be mentioned include: hydrogen, water vapor, methane, ethane, carbon dioxide, nitrogen, argon, or any other inert gas for the dehydrogenation reaction and mixtures thereof. Hydrogen and water vapor are preferably used. A molar ratio (diluent / hydrocarbon chain) of between 0.1:1 and 40:1 is generally used. preferably between 0.4:1 and 10:1.

[0040] The dehydrogenation reaction can be carried out at a temperature between 400°C and 900°C, preferably between 520°C and 650°C.

[0041] The dehydrogenation reaction can be carried out at a pressure of between 0.01 and 10 bars, preferably between 1 and 6, more preferably between 1 and 3 bars.

[0042] The catalyst used is a dehydrogenation catalyst, preferably heterogeneous. It comprises in particular a supported metal.

[0043] More particularly, it comprises at least one metal chosen from groups 6, 8, 9 and 10 of the periodic table of elements (formerly groups VI A and VIII). Preferably, the catalyst comprises a metal chosen from chromium, platinum or palladium; more preferably platinum. The chromium, platinum or palladium present may be the majority metal in the catalyst (by weight, relative to all the metals contained in the catalyst). The catalyst may also comprise other metals such as rhenium, germanium or tin, for example one, two or three metals. The catalyst may also comprise a promoter, preferably a metal chosen from alkali or alkaline earth metals, and preferably potassium.

[0044] According to one embodiment, said catalyst before step a) of introducing the metal M comprises less than 5% by weight of said metal M, preferably less than 1% by weight, relative to the total weight of the catalyst. In particular, the catalyst before step a) of introducing the metal M does not comprise zinc.

[0045] The metal(s) of the above catalyst may be present as element(s) or as compound(s), for example in an oxidized or reduced form. Such catalysts are known to those skilled in the art and are for example described in document US 3,723,557.

[0046] The catalyst support may be of any type known to those skilled in the art and preferably chosen from porous supports. For example, it may be chosen from silica, alumina, silica-alumina, molecular sieves, titanium dioxide and zirconia, preferably alumina.

[0047] A particularly preferred catalyst is a catalyst comprising platinum supported on an alumina, preferably a catalyst consisting essentially of platinum supported on an alumina.

[0048] Such catalysts may undergo activation, for example reduction and / or sulfurization, in situ or ex situ, prior to their use in the dehydrogenation reaction. This operation is known to those skilled in the art and may be carried out according to conventional techniques.

[0049] The reaction can be carried out in one or more reactors. Said reactors can be placed in parallel or in series. The reactors can have fixed catalytic beds, mobile or fluidized. Reactors with moving catalytic beds in series are preferably used.

[0050] In the presence of several reactors, heating means between each reactor can be put in place, so as to ensure that the inlet temperature of the reactants in the reactors is the desired reaction temperature. In this case, the introduction of the metal M can be done before or after the heating means, preferably before.

[0051] After the dehydrogenation reaction, the process according to the invention may comprise other steps up to the recovery of the olefin and hydrogen (H2) produced. In particular, they make it possible to obtain a stream enriched in olefin (streams A and D below), which may be subsequently purified if necessary.

[0052] The outgoing stream S from the reactor may comprise hydrogen, olefin and possibly unreacted hydrocarbon chain. When the reactor has a moving catalytic bed, the heterogeneous catalyst may also be recovered at the reactor outlet separately from the outgoing stream S.

[0053] Once the outgoing flow S has been recovered, its separation can be carried out by any technique known to those skilled in the art. It can, for example, be cooled and then condensed so as to obtain: - a gaseous flow H comprising hydrogen; and - a stream A, preferably liquid, comprising the olefin and possibly the unreacted hydrocarbon chain.

[0054] Stream A can then be recovered and separated so as to obtain: - a liquid stream D comprising the olefin; and - a liquid stream E comprising the unreacted hydrocarbon chain.

[0055] The H and / or E streams can be recycled in whole or in part to the reaction stage. In the presence of several reactors, they can be reintroduced into one, several or all of the reactors. The liquid stream D is recovered and then optionally purified if necessary.

[0056] The dehydrogenation process may also comprise a catalyst regeneration step (called step e)). Indeed, the catalyst may gradually become deactivated, in particular due to the formation of coke on the latter. A regeneration step may therefore prove necessary in order to restore all or part of its activity. This regeneration may be carried out using conventional techniques.

[0057] For example, the catalyst can be regenerated by burning the coke (at at least 600°C) and then carrying out oxychlorination in order to redisperse the catalytic metal. Oxychlorination is generally carried out by contacting the catalyst with a gas comprising a halogen, preferably chlorine, at elevated temperatures, for example between 500°C and 550°C.

[0058] Following the regeneration step, the catalyst can be reduced by contacting with hydrogen, so as to reduce the oxidized metals during regeneration. The regenerated and possibly reduced catalyst can be recycled to the reaction stage, alone or in a mixture with fresh catalyst.

[0059] According to one embodiment, the method according to the invention comprises at least the following steps:

[0060] a) introduction of said metal M upstream or at the inlet of the reactor(s); b) dehydrogenation reaction of the hydrocarbon chain, in the moving catalytic bed reactor(s), so as to obtain an outgoing stream S comprising an olefin and hydrogen;

[0061] c) recovery and separation of the outgoing flow S from step b) so as to obtain:

[0062] - a stream A, preferably liquid, comprising the olefin, and

[0063] - a gaseous H flow comprising hydrogen;

[0064] d) possible recovery of the catalyst;

[0065] e) possible regeneration of said catalyst;

[0066] f) possible recycling to step b) of the regenerated catalyst.

[0067] More particularly, the method according to the invention comprises at least the following steps:

[0068] a) introduction of said metal M upstream or at the inlet of the reactor(s);

[0069] b) dehydrogenation reaction of an alkane, in the catalytic bed reactor(s) mobile lytics, so as to obtain an outgoing stream S comprising an olefin, the unreacted alkane and hydrogen;

[0070] c) recovery and separation of the outgoing flow S from step b) so as to obtain:

[0071] - a stream A, preferably liquid, comprising the olefin and the unreacted alkane, And

[0072] - a gaseous H flow comprising hydrogen;

[0073] d) possible recovery of the catalyst;

[0074] e) possible regeneration of said catalyst;

[0075] f) possible recycling to step b) of the regenerated catalyst;

[0076] g) recovery and separation of stream A to obtain:

[0077] - a stream D comprising the olefin; and

[0078] - a stream E comprising the unreacted alkane;

[0079] h) possible recycling of flow E to step b).

[0080] As indicated above, the H and / or E stream can be recycled in whole or in part to the reaction stage. In the presence of several reactors, it can be reintroduced into one, several or all of the reactors.

[0081] The process according to the invention can be carried out batchwise or continuously, preferably continuously. Several dehydrogenation processes are thus known and those mentioned in the publication “Propylene Production by Propane Dehydro- genation (PDH) (Process Review) by Amir Razmi, 2019 (https: / / www.academia.edu / 39604411 / Propylene_Production_by_Propane_Dehydroge nation_PDH_Process_Review) such as the UOP processes - Honeywell “Oleflex™”, Lummus “CATOFIN®” and “STAR process®” from ThyssenKrupp Uhde.

[0082] The metal M according to the invention is chosen from the group consisting of zinc (Zn), tin (Sn), indium (In), zirconium (Zr), cerium (Ce), germanium (Ge), gallium (Ga), lead (Pb) and thallium (Tl). In particular, the metal M is chosen from the group consisting of zinc (Zn), tin (Sn), lead (Pb) and indium (In). Most preferably, the metal M is zinc (Zn).

[0083] Said metal M is more particularly in the form of an organometallic compound, preferably of the following general formula (II): M [Ra.

[0084] in which: - M is the metal as defined above; - p is an integer between 1 and 6, preferably between 2 and 4; and - the identical or different Rb radicals, independently of each other, represent a hydrocarbon radical containing from 1 to 12 carbon atoms.

[0085] Preferably, the identical or different Rh radicals are chosen independently of one another from the group consisting of:

[0086] a linear, branched or cyclic alkyl containing between 1 and 10 carbon atoms;

[0087] a linear, branched or cyclic alkenyl containing between 1 and 10 carbon atoms;

[0088] an aryl containing between 6 and 10 carbon atoms, said aryl being optionally substituted by one or more alkyl groups, linear or branched, containing from 1 to 10 carbon atoms; and

[0089] an alkylaryl containing between 6 and 12 carbon atoms.

[0090] In particular, the identical or different Rh radicals are chosen independently from each other among the group consisting of:

[0091] a linear, branched or cyclic alkyl containing between 1 and 10 carbon atoms; and

[0092] an aryl containing between 6 and 10 carbon atoms, said aryl being optionally substituted by one or more alkyl groups, linear or branched, containing from 1 to 10 carbon atoms.

[0093] In particular, the identical or different Rh radicals are chosen independently of one another from linear, branched or cyclic alkyls containing between 1 and 10 carbon atoms.

[0094] Preferably, the radicals Ri are identical. Preferably, said alkyls contain between 1 and 6 carbon atoms, more preferably between 1 and 3 carbon atoms. For example, said alkyls are selected from the group consisting of methyl, ethyl, n-propyl and isopropyl. For example, said aryl is phenyl and / or said alkylaryl is benzyl and / or alkenyl is cyclopentadienyl.

[0095] In particular, the organometallic compound is chosen from those of the following formulas:

[0096] Zn(Rj)2 (lia)

[0097] Sn(Rj)4 (Ilb)

[0098] In(Rj)3 (Ile)

[0099] Zr(Rj)4 (Ild)

[0100] Ce^C (Ile)

[0101] Ge(Rj)4 (Ilf)

[0102] Ga(R1)3 (Ilg)

[0103] Pb(Rj)4 (Ilh)

[0104] Tl-Rj (Hi)

[0105] in which the identical or different Rh radicals are as defined for the general formula (II).

[0106] In particular, the metal M is zinc and is found in the form of an organometallic compound of the following general formula (IIa):

[0107] Zn(RÛ2 (lia)

[0108] in which the radicals RB, identical or different, are as defined for the general formula (II).

[0109] The following may be mentioned as organometallic compounds of general formula (II):

[0110] tetramethyl tin, trimethyl indium, tetrabenzyl zirconium, tetraethyl germanium, trimethyl gallium, tetramethyl lead, cyclopentadienyl thallium, dimethyl zinc (Zn(CH3)2), diethyl zinc (Zn(C2H5)2), diisopropyl zinc (Zn(i-C3H7)2), dipropyl zinc (Zn(C3H7)2) and diphenyl zinc (Zn(C6H5)2).

[0111] Said organometallic compound is in particular chosen from the group consisting of: Zn(CH3)2, Zn(C2H5)2, Zn(i-C3H7)2, Zn(C3H7)2 and Zn(C6H5)2. The CAS numbers of these compounds are as follows: Zn(CH3)2: 544-97-8; Zn(C2H5)2: 577-20-0; Zn(C3H7)2: 628-91-1; Zn(i-C3H7)2: 625-81-0 and Zn(C6H5)2: 1078-58-6.

[0112] More preferably, said metallic compound is chosen from Zn(CH3)2, Zn(C2H5)2 and Zn(C3H7)2; more particularly Zn(CH3)2 and Zn(C2H5)2.

[0113] Said organometallic compounds may be formulated in a solvent, in particular an organic solvent, in particular chosen from toluene and alkanes containing between 5 and 10 carbon atoms. Preferably, the solvent is chosen from toluene, heptane, hexane or mixtures thereof. The organometallic compounds as mentioned above are commercially available in the form of solutions at 1 M or 2 M.

[0114] The introduction of the metal M (step a)), optionally in organometallic form as defined above, can be done by any known means, for example by injection.

[0115] It is understood that said metal M is not part of the dehydrogenation catalyst when it is introduced in step a)).

[0116] In particular, said metal M is introduced separately from said dehydrogenation catalyst.

[0117] The introduction may be punctual, semi-continuous or continuous, preferably continuous. It may be carried out at the start-up of an olefin production unit or during all or part of the olefin production. The quantities of metal M introduced may or may not vary during the duration of the addition, for example with a gradient decreasing or increasing during the duration of the addition.

[0118] It is understood that in the case of reactors in series, the introduction of the metal M can be done upstream or at the inlet of the first reactor in the series and / or upstream or at the inlet of any one or more of the following reactors. The introduction of the metal M can thus be done at different locations in the process installations.

[0119] Said metal M, optionally in said organometallic form, is preferably included in a composition also comprising a sulfur compound of the following general formula (I):

[0120] [Chem.l]

[0121] in which: - R is chosen from a linear or branched alkyl radical, containing from 1 to 4 carbon atoms and a linear or branched alkenyl radical, containing from 2 to 4 carbon atoms, - n is an integer equal to 0, 1 or 2, - x is an integer chosen from 0, 1, 2, 3 or 4, and - R' is chosen from a linear or branched alkyl radical, containing from 1 to 4 carbon atoms; a linear or branched alkenyl radical, containing from 2 to 4 carbon atoms, and only when n=x=0, a hydrogen atom.

[0122] Preferably, R and R', identical or different, are chosen from linear or branched alkyls containing from 1 to 4 carbon atoms. Preferably, R and R' are identical.

[0123] In particular, n is equal to 0. In particular, x is chosen from 1, 2, 3 or 4, of preferably 1 or 2 and more preferably 1.

[0124] More particularly, the sulfur compound has the following general formula (la):

[0125] RSS-R' (la),

[0126] in which the radicals R and R' are as defined above.

[0127] It is understood that mixtures of two or more sulfur compounds of general formula (I) may be used according to the present invention. In particular, mixtures of di- and / or polysulfides may be used, for example mixtures of disulfides, such as disulfide oils (called "DSO" for DiSulfide Oils in English).

[0128] Preferably, the sulfur compound of general formula (I) is chosen from dimethyl disulfide (DMDS), dimethyl sulfide (DSM), dimethyl sulfoxide (DMSO) and di-tert-butyl polysulfides. In particular, said sulfur compound of general formula (I) is chosen from dimethyl disulfide (DMDS), dimethyl sulfide (DSM) and di-tert-butyl polysulfides, preferably dimethyl disulfide.

[0129] Most preferably, said sulfur compound is dimethyl disulfide. Said sulfur compound is in particular commercially available. Mention may be made of DMDS Evolution® E2 marketed by the company ARKEMA.

[0130] Particularly preferred are compositions comprising: DMDS; and - an organometallic compound of the following general formula (II):

[0131] M[RJp(n)

[0132] in which M, Ri and p are as defined above.

[0133] In particular, said composition comprises at least 80%, preferably at least 95%, more preferably at least 99% by total weight of sulfur compound(s) relative to the total weight of the composition. It may contain one or more odor masking agents (see, for example, international application WO 2011 / 012815A1).

[0134] Said composition may also comprise a solvent, in particular an organic solvent, in particular chosen from toluene and alkanes containing between 5 and 10 carbon atoms. Preferably, the solvent is chosen from toluene, heptane, hexane or mixtures thereof. Preferably, said composition comprises between 0.001% and 10%, for example between 0.005% and 1.5% by weight of said solvent, relative to the total weight of the composition.

[0135] The quantity of metal M is preferably between 1 and 10,000 ppm, preferably between 1 and 1,000 ppm, for example between 1 and 500 ppm, more preferably between 5 and 200 ppm, relative to the total weight of the sulfur compound(s) and the metal M. It may be between 5 and 100 ppm, more particularly between 10 and 100 ppm relative to the total weight of the sulfur compound and the metal M.

[0136] The quantity of the composition introduced (during step a)) may be between 5 and 200 ppm, preferably between 10 and 90 ppm, for example 25, 50 or 75 ppm relative to the weight of the hydrocarbon chain to be dehydrogenated.

[0137] Said metal M, optionally in organometallic form, or said composition may be premixed with all or part of the hydrocarbon chain to be dehydrogenated before its introduction upstream or at the inlet of the reactor(s).

[0138] The compositions comprising a sulfur compound and a metal M as defined above are new and also form part as such of the present invention.

[0139] Particularly preferred are compositions comprising: DMDS; and - an organometallic compound of the following general formula (II):

[0140] M [RJP (II)

[0141] in which M, Ri and p are as defined above.

[0142] Such compositions are particularly suitable for introduction into the process as according to the invention. They are in particular liquid (at room temperature, for example between 5°C and 40°C). The organometallic compounds are well solubilized in DMDS, which allows great ease of handling and control of the quantity of metal M introduced.

[0143] The compositions according to the invention can be prepared by simple mixing of said sulfur compound and the metal M. Said metal M can be in organometallic form, optionally solubilized in a solvent as defined above.

[0144] They can also be in the form of a kit comprising the sulfur compound and the metal M to be formed upstream, at the inlet or in situ in the dehydrogenation reactor.

[0145] The present invention also relates to the use of said metal M, optionally in organometallic form, in a process for dehydrogenating a hydrocarbon chain into olefin, preferably to increase the yield thereof. It is understood that said metal M may be included in a composition as defined above. DESCRIPTION OF THE FIGURES

[0146] [Fig. 1] represents the yield of the dehydrogenation reaction obtained as a function of time.

[0147] DMDS alone is represented by the curve containing the squares, DMDS with Zn(CH3)2 added is represented by the continuous curve and DMDS with Zn(C2H5)2 added is represented by the curve containing the diamonds. EXAMPLES Example 1: Method according to the invention

[0148] The dehydrogenation of propane is carried out in a reactor at a temperature of 625°C, at a pressure of 3 bars and in the presence of a Pt / Al2O3 type catalyst (Pt / Al2O3 catalyst from Strem Chemicals Inc.) on a fixed bed over a period of 20 h.

[0149] The propane flow rate is 2.2 NL / h.

[0150] A continuous injection of 75 ppm of different DMDS compositions is carried out upstream of the reactor.

[0151] Compositions according to the invention were prepared by adding to DMDS, 50 ppm of the following commercial solutions (supplier Aldrich): - an IM solution of dimethyl zinc, - an IM solution of diethyl zinc.

[0152] Clear solutions of additive DMDS are obtained.

[0153] A comparative composition of DMDS without the addition of metal M is also tested.

[0154] The results obtained are given by [Fig.l].

[0155] The cumulative quantities of propylene obtained at 8 p.m. are as follows: - 6.08 NL with DMDS alone; - 6.23 NL with DMDS supplemented with Zn(CH3)2>, i.e. an increase in final yield of 2.6%; and - 6.37 NL with DMDS added with Zn(C2H5)2, i.e. an increase in final yield of 4.8%.

[0156] The propylene yield is therefore improved thanks to the present invention.

Claims

Claims

1. Process for the preparation of an olefin comprising a step of dehydrogenation of a hydrocarbon chain, in at least one reactor in the presence of a catalyst; said process comprising a step of introducing a metal M upstream or at the inlet of the reactor(s), and said metal M being in the form of an organometallic compound of the following general formula (II): M[RJP (II) in which: - M being chosen from the group consisting of zinc (Zn), tin (Sn), indium (In), zirconium (Zr), cerium (Ce), germanium (Ge), gallium (Ga), lead (Pb) and thallium (Tl), preferably zinc; - p is an integer between 1 and 6, preferably between 2 and 4; and - the radicals Rh, which are identical or different, represent, independently of each other, a hydrocarbon radical containing from 1 to 12 carbon atoms.

2. The method of claim 1, wherein said organometallic compound is selected from the group consisting of: tetramethyl tin, trimethyl indium, tetrabenzyl zirconium, tetraethyl germanium, trimethyl gallium, tetramethyl lead, cyclopentadienyl thallium, dimethyl zinc, diethyl zinc, diisopropyl zinc, dipropyl zinc and diphenyl zinc.

3. Process according to any one of the preceding claims, in which the metal M is included in a composition also comprising a sulfur compound of the following general formula (I): [Chem.l] R..... law (I) in which: - R is chosen from a linear or branched alkyl radical, containing from 1 to 4 carbon atoms and a linear or branched alkenyl radical, containing from 2 to 4 carbon atoms, - n is an integer equal to 0, 1 or 2, - x is an integer chosen from 0, 1, 2, 3 or 4, and - R' is chosen from a linear or branched alkyl radical, containing from 1 to 4 carbon atoms; a linear or branched alkenyl radical, containing from 2 to 4 carbon atoms, and only when n=x=0, a hydrogen atom.

4. A method according to claim 3, wherein said sulfur compound of general formula (I) is selected from dimethyl disulfide (DMDS), dimethyl sulfide (DSM) and di-tert-butyl polysulfides, preferably dimethyl disulfide.

5. A method according to any preceding claim, comprising at least the following steps: a. introduction of the metal M as defined in any one of claims 1 to 5 upstream or at the inlet of the reactor(s); b. dehydrogenation reaction of the hydrocarbon chain in the moving catalytic bed reactor(s), so as to obtain an outgoing stream S comprising an olefin and hydrogen; c. recovery and separation of the outgoing flow S from step b) so as to obtain: - a stream A comprising the olefin, and - an H stream comprising hydrogen, d. possible recovery of the catalyst; e. possible regeneration of said catalyst; and f. possible recycling to step b) of the regenerated catalyst.

6. Composition comprising: a sulfur compound of the following general formula (I): [Chem.l] R-St-Sx-R' (D in which: - R is chosen from a linear or branched alkyl radical, containing from 1 to 4 carbon atoms and a linear or branched alkenyl radical, containing from 2 to 4 carbon atoms, - n is an integer equal to 0, 1 or 2, - x is an integer chosen from 0, 1, 2, 3 or 4, and - R' is chosen from a linear or branched alkyl radical, containing from 1 to 4 carbon atoms; a linear or branched alkenyl radical, containing from 2 to 4 carbon atoms, and only when n=x=0, a hydrogen atom; and • a metal M in the form of an organometallic compound of the following general formula (II): M[RJp (II) in which: - M being chosen from the group consisting of zinc (Zn), tin (Sn), indium (In), zirconium (Zr), cerium (Ce), germanium (Ge), gallium (Ga), lead (Pb) and thallium (Tl), preferably zinc; - p is an integer between 1 and 6, preferably between 2 and 4; and - the identical or different Rh radicals represent, independently of each other, a hydrocarbon radical containing from 1 to 12 carbon atoms;and said composition comprising at least 99% by total weight of sulfur compound(s) relative to the total weight of the composition.;

7. Composition according to claim 6, wherein said sulfur compound of general formula (I) is chosen from dimethyl disulfide (DMDS), dimethyl sulfide (DSM) and di-tert-butyl polysulfides, preferably dimethyl disulfide.

8. A composition according to any one of claims 6 or 7, also comprising an organic solvent.

9. Use of a composition as defined in any one of claims 6 to 8, in a process for dehydrogenating a hydrocarbon chain into olefin.

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