Alkanes are products which are generally difficult to employ in reactions because of their high chemical inertia and are essentially used as fuels and energetic materials.

Numerous studies have been carried out with the aim of converting alkanes to their lower homologues, in particular by hydrogenolysis reactions, that is to say reactions in which a carbon-carbon bond is split and hydrogen is added to each portion.

These reactions are carried out by bringing alkanes into contact with hydrogen in the presence of a hydrogenolysis catalyst generally chosen from catalysts based on transition metals, provided in particular in a bulk form or in the form of metal films or particles, in particular supported on oxides.

More recently, a need has made itself felt to convert alkanes to their higher homologues, in particular with the aim of enhancing in value light alkanes and in particular methane. Such conversions can be obtained by homologation reactions which make it possible to convert light alkanes to heavier alkanes, in particular by virtue of metal catalysts capable of carrying out reactions in which carbon-carbon bonds and optionally carbon-metal and carbon-hydrogen bonds are split and recombined. Various processes are provided for carrying out such reactions. In particular, the metathesis of alkane (s) to higher and lower homologues can be carried out according to the process disclosed in International Patent Application WO 98/02244. The cross-metathesis of alkane (s) in the presence of an organometallic compound can also be carried out according to the process disclosed in International Patent Application WO 00/27781.

The incorporation of methane into alkane (s) can also be carried out according to the process disclosed in International Patent Application WO 01/0477. It has been pointed out that the catalytic activity of these homologation reactions gradually decreases over time, probably by an ageing or deactivating effect on the catalysts used.

United States Patent US 5 414 176 discloses a process for the conversion of methane to higher hydrocarbons, in particular to C2 to C5 alkanes, in the presence of a known catalyst as hydrogenolysis catalyst comprising in particular a transition metal dispersed over a support based on a refractory oxide. The process is based on a fundamental cycle of operations which are repeated continually and uniformly over an extremely short cycle time ranging from 12 to 480 seconds. The fundamental cycle comprises bringing the catalyst into contact successively with a stream of methane and then a stream of hydrogen. The operations in which the catalyst is brought into contact with these two streams make it possible to carry out the adsorption and the conversion of the methane, and then the desorption of the products obtained. It is specified that all the alkanes which are thus produced are adsorbed in the form of olefins and that the stream of hydrogen makes it possible to convert the olefins to alkanes. Thus, the hydrogen used in this process is involved as reactant in the manufacture of the higher hydrocarbons. Not the slightest mention is made of this process meeting a need to activate the catalyst, which would be gradually subjected to ageing over time.

An improved and in particular more efficient process for the manufacture of alkanes has now been found. It makes possible the more effective use of metal catalysts capable in particular of carrying out reactions for the splitting and recombination of carbon-carbon bonds and optionally of carbon-metal and carbon-hydrogen bonds, in particular catalysts for alkane metathesis, alkane cross-metathesis and/or alkane "methane-olysis" (i. e. incorporation of methane into alkane (s) ). This process makes it possible to reduce or to slow down the ageing or the deactivation of these catalysts, or to maintain the activity of these catalysts in reactions for alkane metathesis, alkane cross-metathesis and/or alkane methane-olysis at levels in particular higher than those normally expected in such reactions in the absence of any treatment of these catalysts, or even to regenerate or to reactivate these catalysts, during the manufacture of alkanes.

A subject-matter of the invention is a process for the manufacture of alkanes comprising an operation in which at least one starting alkane is brought into contact with a metal catalyst comprising at least one metal, Me, bonded to at least one hydrogen

atom and/or to at least one hydrocarbon radical, characterized in that the catalyst is brought into contact with an agent which forms hydrogen"in situ", in the manufacture of alkanes.

Another subject-matter of the invention is a process for the activation of a metal catalyst intended to manufacture alkanes and comprising at least one metal, Me, bonded to at least one hydrogen atom and/or to at least one hydrocarbon radical, which process is characterized in that, during the manufacture of alkanes carried out by bringing the catalyst into contact with at least one starting alkane, the catalyst is brought into contact with an agent which forms hydrogen"in situ".

The term"activation of a catalyst"can also generally comprise, according to the present invention, regenerating or reactivating the catalyst, or maintaining the activity of the catalyst in reactions for alkane metathesis, alkane cross-metathesis and/or alkane methane-olysis at levels higher than those expected in such reactions in the absence of any treatment of the catalyst, or sustaining the activity of the catalyst over time in the said reactions, e. g. by reducing the rate of the deactivation of the catalyst over time during the manufacture of alkanes.

Figure 1 is a diagrammatic representation of a device which makes it possible to implement the process according to the invention, in which the manufacture of alkanes and the activation of the catalyst by an agent which forms hydrogen"in situ"take place simultaneously and preferably continuously in a single zone.

Figure 2 is a diagrammatic representation of an improved device in comparison with that illustrated in Figure 1 which makes it possible to implement the process according to the invention and which comprises in particular a single gas-phase zone.

Figure 3 is a diagrammatic representation of a device which makes it possible to implement the process according to the invention, in which the manufacture of alkanes and the activation of the catalyst by an agent which forms hydrogen"in situ"take place simultaneously and preferably continuously in two separate zones.

Figure 4 is a diagrammatic representation of an improved device in comparison with that illustrated in Figure 3 which makes it possible to implement the process according to the invention, in which the manufacture of alkanes and the activation of the catalyst are carried out in two separate gas phase zones.

According to the present invention, the manufacture of alkanes comprises bringing at least one starting alkane into contact with a catalyst. The starting alkane (s)

can be chosen from linear alkanes and branched alkanes, for example from linear Ca to C80, preferably C2 to C30, in particular Ca to C20, especially C2 to C17, alkanes, from linear C18 to C80, preferably C21 to C80, in particular C31 to C80, alkanes, from branched C4 to C80, preferably C4 to C30, in particular C4 to C20, especially C4 to C17, alkanes and from branched Cis to Cgo) preferably C21 to C80, in particular C31 to C80, alkanes. The linear or branched Cis to Cso, preferably C21 to C80, in particular C31 to Cgo, alkanes generally constitute what are known as waxes, in particular petroleum waxes, such as linear or branched paraffin waxes (or linear or branched macrocrystalline waxes) or linear or branched microcrystalline waxes, and synthetic waxes, such as"Fischer- Tropsch"waxes and polyolefin waxes, for example polyethylene waxes, polypropylene waxes, poly-a-olefin waxes and poly (heavy a-olefin) waxes. The linear or branched alkanes generally correspond to the general formula : CnH2n+2 (1) in which n is a number ranging from 2 to 80, preferably from 2 to 30, in particular from 2 to 20, especially from 2 to 17, or from 18 to 80, preferably from 21 to 80, in particular from 31 to 80, or from 4 to 80, preferably from 4 to 30, in particular from 4 to 20, especially from 4 to 17.

The starting alkane (s) can also be chosen from cycloalkanes substituted by at least one linear or branched alkane chain, for example from the said substituted C4 to Cgo, preferably C4 to C60, cycloalkanes, or from the said substituted C4 to C30, preferably C4 to C20, in particular C4 to Cl7, cycloalkanes, and from the said substituted Cl8 to C80, preferably C21 to Cgo, especially C31 to C80, cycloalkanes. The term"cycloalkanes"is generally understood to mean cycloparaffins or cyclanic hydrocarbons, or cyclic alkanes, in particular mono-or bi-or polycyclic alkanes. Use may in particular be made, among substituted cycloalkanes, of those having at least one linear or branched alkane chain having from 1 to 12, preferably from 1 to 6, carbon atoms. The substituted cycloalkanes and in particular the substituted monocyclic alkanes can correspond to the general formula: CmH2m (2)

in which m is a number ranging from 4 to 80, preferably from 4 to 60, in particular from 4 to 30, especially from 4 to 20 or from 4 to 17, or alternatively from 18 to 80, preferably from 21 to 80, in particular from 31 to 80.

The substituted cycloalkanes and in particular the substituted monocyclic alkanes can also correspond to the general formula: (CH2)x-CH-(CH2)y-CH3 (3) # in which x is a number equal to or greater than 2, preferably ranging from 2 to 20, and y is a number equal to or greater than 0, preferably ranging from 0 to 58, in particular from 0 to 28.

Use may be made, among substituted cycloalkanes, of methylcyclohexane, ethylcyclohexane, n-propylcyclohexane, isopropylcyclohexane, n-butylcyclohexane, isobutylcyclohexane and derivatives of decahydronaphthalene which are substituted by at least one linear or branched alkane chain, it being possible for the said chain to have from 1 to 12, preferably from 1 to 6, carbon atoms.

The starting alkane (s) can also be chosen from methane and mixtures of methane with at least one of the other starting alkanes mentioned above, in particular one or more other alkanes chosen from linear alkanes, branched alkanes or substituted cycloalkanes, such as those mentioned above.

The starting alkane (s) can be preferably chosen from ethane, propane, n-butane, isobutane, n-pentane, isopentane, n-hexane, isohexane, 2-methylpentane, 3- methylpentane, 2,3-dimethylbutane, n-heptane, isoheptane, n-octane and isooctan, and from methane and mixtures of methane with at least one of the starting alkanes mentioned above.

The starting alkane (s) can be chosen in particular from liquefied petroleum gas or LPG (mixtures of propane and butanes), natural gas (a mixture essentially comprising methane), wet gas or wet natural gas (a mixture of methane and of higher homologues of methane, such as C2 to C5 or C3 to C4 alkanes, in particular a mixture of methane and propane), natural-gas liquids or NGL (mixtures of ethane, propane, butanes, pentanes, natural gasoline and condensates), and syncrude (a mixture of C5 and higher alkanes, in particular a mixture of C5 alkanes).

In one of the alternative forms of the process according to the invention, the

manufacture of alkanes which results from bringing at least one starting alkane into contact with the catalyst, can be carried out by subjecting, preferably as main stage, the starting alkane (s) (e. g. the linear or branched alkanes or the substituted cycloalkanes mentioned above) to a reaction for the metathesis of carbon-carbon bonds, in the presence of the catalyst and optionally of at least one other starting alkane, in particular according to the process disclosed in International Patent Application WO 98/02244. In particular, it can be a matter of reacting the linear or branched alkane or the substituted cycloalkane by a metathesis reaction with itself, to produce the higher and lower homologous alkanes. It can also be a matter of reacting together at least two different starting alkanes chosen from linear or branched alkanes or substituted cycloalkanes, so as to obtain the higher and lower homologous alkanes resulting from reactions for the metathesis of carbon-carbon bonds. In this case, the metathesis reaction is carried out with a mixture of at least two different starting alkanes. In the reactions for the metathesis of one or more starting alkanes, it is preferable to use a catalyst comprising at least one metal, Me, bonded in particular to at least one hydrogen atom and/or to at least one hydrocarbon radical. The metathesis reaction can be generally carried out at a temperature ranging from 25 to 600°C, preferably from 25 to 500°C, or from 25 to 400°C, in particular from 25 to 300°C, or from 100 to 200°C, and in particular under an absolute pressure ranging from 10-3 to 10 MPa. It is preferably carried out continuously.

In another alternative form of the process according to the invention, the manufacture of alkanes can be carried out by subjecting, preferably as main stage, the starting alkane (s) (e. g. the linear or branched alkanes or the substituted cycloalkanes mentioned above) to an alkane cross-metathesis reaction comprising bringing the starting alkane (s) into contact with the catalyst comprising at least one metal, Me, bonded to at least one hydrocarbon radical, so as in particular to obtain at least one final alkane which is a higher or lower homologue of the starting alkane (s). The cross- metathesis reaction can be carried out according to the process described in International Patent Application WO 00/27781. Generally, the cross-metathesis reaction is obtained in particular by splitting the hydrocarbon radical from the catalyst and recombining the said radical with at least one other radical originating from splitting of the starting alkane (s). The cross-metathesis reaction can be generally carried out at a temperature ranging from 20 to 600°C, or from 20 to 500°C, preferably from 20 to 400°C, or from 100 to 300°C, and in particular under an absolute pressure ranging from

10-3 to 10 MPa. It is preferably carried out continuously.

In another alternative form of the process according to the invention, the manufacture of alkanes can be carried out, preferably as main stage, by bringing methane and one or more other starting alkanes (e. g. the linear or branched alkanes or the substituted cycloalkanes mentioned above), in particular having at least 3 carbon atoms, into contact with the catalyst. In this case, the starting alkanes employed in the manufacture of alkanes comprise methane and at least one of the other starting alkanes, such as those described above. The contacting operation can be carried out in particular by employing a mixture of methane with at least one of the other starting alkanes, such as those described above and in particular Cz to C6, or C2 to C5, or C2 to C4, or C3 to C6, or C3 to Cs, or C3 to C4, or C4 to C6, or C4 to C5, or C5 to C6, or C5 alkanes, for example a mixture, such as natural gas, wet gas or wet natural gas, or a mixture of natural gas with LPG, NGL or syncrude. The contacting operation can subsequently comprise bringing this mixture into contact with the catalyst. The contacting operation can be carried out so as to form at least one final alkane having a number of carbon atoms equal to or greater than 2, in particular according to the process described in International Patent Application WO 01/0477. The reaction which results, according to this process, from bringing methane into contact with at least one other starting alkane and from the incorporation of methane into the other starting alkane (s) is generally known as the"methane-olysis"reaction. The contacting operation can be generally carried out at a temperature ranging from-30°C to + 600°C, preferably from-30°C to + 500°C, in particular from-30°C to + 400°C, or from 0 to 300°C, for instance from 20 to 200°C, and in particular under an absolute pressure ranging from 10-3 to 50 or 100 MPa, or from 10-3 to 30 MPa, preferably from 10-l to 20 MPa, in particular from 10-l to 10 MPa. The manufacture of alkanes resulting from the methane-olysis reaction is particularly advantageous when the contacting operation is carried out under a methane partial pressure equal to or greater than 0.1 MPa, preferably chosen within a range from 0.1 to 100 MPa, in particular from 0.1 to 5, 0 MPa, especially from 0.1 to 30 MPa or from 0.2 to 20 MPa. Use may be made of a catalyst capable of catalysing a reaction for the splitting and/or recombination of carbon-carbon bonds and/or carbon-hydrogen bonds and/or carbon-metal bonds. The manufacture of alkanes is preferably carried out continuously.

In another alternative form of the process according to the invention, the

manufacture of alkanes can be carried out, preferably as main stage, by bringing methane into contact with the catalyst, preferably comprising at least one metal, Me, chosen from the transition metals, the lanthanides and the actinides. In this case, the starting alkane is composed of methane. It results from this contacting operation that the methane reacts essentially with itself by a coupling reaction of the methane. The contacting operation is preferably carried out so as to form ethane, with in particular a selectivity for ethane of at least 65 % by weight with respect to the carbon-containing products formed during the manufacture of alkanes. It can be generally carried out at a temperature ranging from-30°C to + 800°C, preferably from 0 to 600°C, in particular from 20 to 500°C and in particular from 50 to less than 450°C, for example from 50 to 400°C or from 50 to 350°C, and in particular under a total absolute pressure ranging from 10-3 to 100 MPa, preferably from 0.1 to 50 MPa, in particular from 0.1 to 30 MPa, or from 0.1 to 20 MPa, especially from 0.1 to 10 MPa. It is preferably carried out continuously.

The manufacture of alkanes as described in one of the preceding alternative forms can be carried out in the presence of one or more inert agents, preferably of more or more liquid or gaseous inert agents, in particular of one or more inert gases, such as nitrogen, helium or argon. Furthermore, it can be carried out either batchwise or, preferably, continuously.

The Periodic Table of the Elements mentioned below is that proposed by the IUPAC in 1991 and which is found, for example, in"CRC Handbook of Chemistry and Physics", 76th Edition (1995-1996), by David R. Lide, published by CRC Press Inc.

(USA).

According to the present invention, the catalyst is brought into contact with an agent which forms hydrogen"in situ", during the manufacture of alkanes. It has been observed in particular that such a contacting operation has the effect of slowing down or reducing the ageing or the deactivation of the catalyst over time, or maintaining the activity of the catalyst during the manufacture of alkanes at levels higher than those expected in the absence of any treatment of the catalyst.

The agent which forms hydrogen"in situ"can preferably be chosen from agents capable of releasing hydrogen, in particular by a physical action, such as a desorption, and from agents capable of forming hydrogen by a chemical reaction, in particular in the presence of the catalyst. The formation of hydrogen"in situ"can be carried out by

bringing the agent into contact with the catalyst. In practice, the operation of bringing the catalyst into contact with the agent can be carried out by addition of the agent to the catalyst, or by addition of the catalyst to the agent, or by simultaneous additions of the catalyst and of the agent. The agent can be provided in a solid, liquid or gaseous form.

Use may be made, among the agents which form hydrogen"in situ", of agents capable of releasing hydrogen, in particular by a physical action, such as a desorption.

These agents can be solids comprising in particular hydrogen absorbed or adsorbed on themselves. They can be chosen from metals or metal alloys capable of reversibly accumulating hydrogen (and therefore in particular of restoring at least a portion of the accumulated hydrogen), and preferably from metal hydrides and in particular from metal alloy hydrides, in particular in the bulk form (especially in the form unsupported on or non-dispersed over a solid support). The metals involved in particular in these metal hydrides and especially in these metal alloy hydrides can be chosen from the lanthanides, the actinides and the metals from Groups 2 to 12, preferably 2 to 11, of the Periodic Table of the Elements, in particular the transition metals from Groups 3 to 11, preferably from Groups 3 to 10, of the said Table. More particularly, the metal hydrides can be chosen from binary hydrides and intermetallic hydrides (or metal alloy hydrides).

The term"binary hydride"is generally understood to mean a metal hydride which can correspond to the general formula: M-MHn (5) in which M represents a metal as defined above, H represents a hydrogen atom and n is an integer or fractional number in particular greater than 0 and equal to or less than 6 generally. The reticular structure of binary hydrides can typically be that of a metal with hydrogen atoms embedded in the metal lattice. Binary hydrides are also known as interstitial hydrides. Binary hydrides can in particular be chosen from lanthanide hydrides, actinide hydrides and hydrides of metals from Groups 2 to 12, in particular from magnesium hydrides, titanium hydrides, zirconium hydrides, palladium hydrides, ruthenium hydrides and platinum hydrides.

Use may also be made of intermetallic hydrides (or metal alloy hydrides), in particular of hydrides of alloys of transition metals from Groups 3 to 11 with optionally other metals from Groups 2,12 and 13 of the Periodic Table of the Elements. The term

"intermetallic hydride" (or"metal alloy hydride") is generally understood to mean an at least ternary hydride which can correspond to the general formula: M'x My Hz (6) in which M'and M"represent two different metals as defined above, H represents a hydrogen atom and x, y and z represent identical or different integers or fractional numbers generally greater than 0 and equal to or less than 6. More particularly, the intermetallic hydrides (or metal alloy hydrides) can be chosen from iron/titanium hydrides, lanthanum/nickel hydrides, calcium/nickel hydrides, europium/ruthenium hydrides, magnesium/nickel hydrides, zirconium/manganese hydrides, lanthanum/nickel/aluminium hydrides, titanium/vanadium/iron/manganese hydrides and titanium/zirconium/vanadium/iron/chromium/manganese hydrides.

In the specific case where the manufacture of alkanes employs methane as sole starting alkane, the agent which forms hydrogen"in situ"used to activate the catalyst is preferably chosen from agents capable of releasing hydrogen in particular by a physical action, such as a desorption, in particular from the metal hydrides described above.

The formation of hydrogen"in situ"can thus be carried out by subjecting one of these agents capable of releasing hydrogen to a temperature and/or a pressure such that the agent releases the hydrogen, in particular in the presence of the catalyst.

Use may also be made, among the agents which form hydrogen"in situ", of agents (or reactants) capable of forming hydrogen by a chemical reaction, in particular by a spontaneous chemical reaction in the presence of the catalyst. These agents can be provided in the liquid or gaseous form. Preference is given, among these agents, to methane, in particular when it is used in the presence of the catalyst. In particular, it is observed that methane, brought into contact with the catalyst, can form hydrogen and ethane"in situ"by a, preferably non-oxidizing, coupling reaction of methane.

The amount of the agent which forms hydrogen"in situ"employed with the catalyst is chosen so that it is sufficient to reactivate (or to regenerate) the catalyst, or to reduce or to slow down the loss in activity (or the deactivation) of the catalyst during the manufacture of alkanes, or to maintain the activity of the catalyst in the manufacture of alkanes at a higher level than that expected in the absence of any treatment of the catalyst. The amount of the agent which forms hydrogen"in situ"can be such that the

amount of the hydrogen thus produced"in situ"leads to the formation of a hydrogen partial pressure ranging from 104 to 10-1 MPa, preferably from 10-3 to 10-1 MPa, in the medium in which the catalyst is brought into contact with the said agent. When the agent which forms hydrogen"in situ"is used in the presence of the starting alkane (s), the amount of the hydrogen produced"in situ"can be such that the molar ratio of the hydrogen produced"in situ"to the starting alkane (s) is from 10-6/1 to 10''/1, in particular from 10-5/1 to 10-2/l.

The operation in which the catalyst is brought into contact or activated with the agent which forms hydrogen"in situ"can be carried out at a temperature ranging from- 30°C to 800°C, preferably from 0 to 600°C, in particular from 20 to 500°C, especially 20 to 400°C. The total absolute pressure during the contacting operation can be from 10- 3 to 102 MPa, preferably from 0.1 to 50 MPa. The duration of the contacting operation depends in particular on the temperature and on the pressure exerted during this contacting operation and on the nature of the agent which forms hydrogen"in situ". The duration of the operation can be at least 1 minute, preferably at least 10 minutes, in particular at least 30 minutes, and can range up to 72 hours, preferably up to 48 hours, and in particular can be at most equal to the duration of the manufacture of alkanes, in particular when this contacting operation is carried out in the presence of the starting alkane (s).

The operation in which the catalyst is brought into contact with the agent which forms hydrogen"in situ", can be carried out either in the presence or in the absence of the starting alkane (s) used in particular in the manufacture of alkanes. The term "starting alkane (s)" is understood in particular to mean methane and/or the starting alkane (s), such as the linear or branched alkanes or the cycloalkanes described above used in particular in the manufacture of alkanes. The operation in which the catalyst is brought into contact with the agent which forms hydrogen"in situ", can furthermore be carried out either batchwise or, preferably, continuously. It can also be carried out in the presence of one or more inert agents, in particular of one or more liquid or gaseous inert agents, especially of one or more inert gases, such as nitrogen, helium or argon.

The operation in which the catalyst is brought into contact with the agent which forms hydrogen"in situ"can advantageously be carried out in the presence of the starting alkane (s) used in particular in the manufacture of alkanes. This means that the catalyst is brought into contact simultaneously with the agent and the starting alkane (s).

This also means that the contacting operation for the catalyst is carried out so that the manufacture of alkanes and the contacting or activation of the catalyst with the agent are carried out together and simultaneously, and that the zone in which the catalyst is brought into contact or activated with the agent corresponds to or is coincident with the reaction zone for the manufacture of alkanes. In practice, the process of the invention can comprise the additions of starting alkane (s) and of the agent which forms hydrogen "in situ"to the catalyst. These additions can preferably be carried out simultaneously and/or continuously. In the specific case where methane is the only starting alkane used in the manufacture of alkanes, the agent which forms hydrogen"in situ"is preferably chosen from agents capable of releasing hydrogen, in particular by a physical action, such as a desorption.

In a batchwise manufacture of alkanes, the operation in which the catalyst is brought into contact or activated with the agent which forms hydrogen"in situ"can be carried out batchwise in the presence of the starting alkane (s). In this case, the manufacture of alkanes and the contacting or the activation of the catalyst are carried out together and simultaneously, and batchwise in the same zone. In practice, it is possible, for example, to add the starting alkane (s) and the agent, preferably simultaneously, batchwise to the catalyst. It is also possible to add the starting alkane (s) batchwise to the catalyst brought into contact batchwise with the agent. It is also possible, conversely, to carry out continuously the operation in which the catalyst is brought into contact or activated with the agent. In the latter case, it is possible to carry out batchwise or sequential additions of the starting alkane (s) to the catalyst, while simultaneously the agent is added continuously to the said catalyst. It is also possible to bring the catalyst into contact continuously with the agent, while batchwise or sequential additions of the starting alkane (s) to the catalyst and to the agent thus brought into continuous contact are carried out.

However, it is preferable to manufacture the alkanes continuously. When, in a continuous manufacture of alkanes, the operation in which the catalyst is brought into contact or activated with the agent which forms hydrogen"in situ", is carried out in the presence of the starting alkane (s), it can be carried out continuously. In practice, in this case, continuous and simultaneous additions of the starting alkane (s) and of the agent to the catalyst can be carried out. A continuous addition of the starting alkane (s) to the catalyst brought into continuous contact with the agent can also be carried out.

Conversely, when, in a continuous manufacture of alkanes, the operation in which the catalyst is brought into contact or activated with the agent, is carried out in the presence of the starting alkane (s), it can be carried out batchwise. In practice, in the latter case, batchwise or sequential additions of the agent to the catalyst can be carried out, while simultaneously the starting alkane (s) is (are) added continuously to the said catalyst.

Such batchwise or sequential additions can be carried out regularly over time, or so that during the continuous manufacture of alkanes, the activity of the catalyst is maintained at a predetermined level, or at a level higher than that expected in the absence of any treatment of the catalyst, or the rate of the deactivation of the catalyst over time is reduced.

It is also possible, conversely, for the operation in which the catalyst is brought into contact with the agent which forms hydrogen"in situ", to be carried out in the absence of the starting alkane (s). This means that the catalyst brought into contact with the starting alkane (s) in the manufacture of alkanes is separated from the alkanes, in particular from the unreacted starting alkane (s) and from the alkanes produced, before it is brought into contact with the agent which forms hydrogen"in situ". The zone in which the catalyst is brought into contact or activated with the agent can be identical to or more generally different from the reaction zone where the alkanes are manufactured.

If, however, the zone is identical, this means that the same zone can operate alternately to manufacture alkanes and to activate the catalyst. It is also possible, according to one alternative form, to employ at least two separate zones containing the catalyst, zones which operate in parallel and in a way which alternates and is offset in time between manufacture of alkanes and activation of the catalyst. Thus, for example, in the case where each zone simultaneously operates in parallel and alternately in the manufacture of alkanes and in the activation of the catalyst, by bringing the catalyst into contact respectively with the starting alkane (s) and with the agent which forms hydrogen"in situ", the first zone can operate in the manufacture of alkanes, while the second zone simultaneously operates in the activation of the catalyst, and then vice versa, when each zone alternates between manufacture and activation. The stage when each zone alternates, can be carried out by maintaining the catalyst in each zone, but by replacing the agent which forms hydrogen"in situ"with the starting alkane (s) and vice versa respectively in each zone, or by maintaining the agent and the starting alkane (s) in their respective zone, but by transferring the catalyst from one zone to the other zone. Such a

process is particularly advantageous when it is carried out continuously.

When, in a batchwise process for the manufacture of alkanes, the operation in which the catalyst is brought into contact or activated with the agent which forms hydrogen"in situ", is carried out in the absence of the starting alkane (s), it can be carried out just as easily batchwise as continuously. In the case of an operation in which the catalyst is brought into contact or activated with the agent under batchwise conditions, the process can comprise the following successive stages, carried out in particular in a repetitive way: (a) the catalyst brought into contact with the starting alkane (s) is recovered at the end of a batchwise manufacture of alkanes, (b) the catalyst thus recovered is separated from the alkanes, in particular from the unreacted starting alkane (s) and from the alkanes produced, (c) the catalyst thus separated is brought into contact or activated with the agent which forms hydrogen"in situ"under batchwise conditions, (d) the catalyst thus contacted or activated is optionally separated from the agent and/or from the hdyrogen produced"in situ"at the end of the batchwise contacting or activating operation, and (e) the catalyst is brought back into contact with the starting alkane (s) in another batchwise manufacture of alkanes.

When, in a batchwise process for the manufacture of alkanes, the operation in which the catalyst is brought into contact or activated with the agent which forms hydrogen"in situ", is carried out in the absence of the starting alkane (s), it can be carried out continuously. In this case, the process can comprise the following successive stages, carried out in particular in a repetitive way: (a) the catalyst brought into contact with the starting alkane (s) is recovered at the end of a batchwise manufacture of alkanes, (b) the catalyst thus recovered is separated from the alkanes, in particular from the unreacted starting alkane (s) and from the alkanes produced, (c) the catalyst thus separated is added to and mixed with a portion of the catalyst in continuous contact or continuously activated with the agent which forms hydrogen"in situ", so as in particular to activate the catalyst, (d) a portion of the catalyst thus brought into continuous contact or continuously activated is withdrawn and recovered, (e) the portion of the catalyst thus withdrawn and recovered is optionally separated from the agent and/or from the hydrogen produced"in situ", and (f) the portion of the catalyst is brought into contact with the starting alkane (s) in another batchwise manufacture of alkanes.

It is generally preferable to manufacture the alkanes continuously. Thus, when, in a continuous process for the manufacture of alkanes, the operation in which the

catalyst is brought into contact or activated with the agent which forms hydrogen"in situ", is carried out in the absence of the starting alkane (s), it can be carried out either batchwise or, preferably, continuously. In the case where the catalyst is brought into contact or activated with the agent under batchwise conditions, the process can comprise the following successive stages, carried out in particular in a repetitive way: (a) a portion of the catalyst brought into contact with the starting alkane (s) in a continuous manufacture of alkanes is withdrawn and recovered, (b) the portion of the catalyst thus withdrawn and recovered is separated from the alkanes, in particular from the unreacted starting alkane (s) and from the alkanes produced, (c) the portion of the catalyst thus separated is brought into contact or activated with the agent which forms hydrogen"in situ"under batchwise conditions, (d) the portion of the catalyst thus brought into contact or activated is optionally separated from the agent and/or from the hydrogen produced"in situ"at the end of the batchwise contacting or activating operation, and (e) the portion of the catalyst is brought back into contact with the starting alkane (s) in the continuous manufacture of alkanes.

When, in a continuous process for the manufacture of alkanes, the operation in which the metal catalyst is brought into contact or activated with the agent which forms hydrogen"in situ", is carried out in the absence of the starting alkane (s), it can be carried out continuously. In this case, the process can comprise the following successive stages, carried out in particular in a repetitive way: (a) a portion of the catalyst brought into contact with the starting alkane (s) in a continuous manufacture of alkanes is withdrawn and recovered, (b) the portion of the catalyst thus withdrawn and recovered is separated from the alkanes, in particular from the unreacted starting alkane (s) and from the alkanes produced, (c) the portion of the catalyst thus separated is added to and mixed with a portion of the catalyst in continuous contact or continuously activated with the agent which forms hydrogen". in situ", so as in particular to activate the catalyst, (d) a portion of the catalyst thus brought into continuous contact or continuously activated is withdrawn and recovered, (e) the portion of the catalyst thus withdrawn and recovered is optionally separated from the agent and/or from the hydrogen produced"in situ", and (f) the portion of the catalyst is brought into contact with the starting alkane (s) in the continuous manufacture of alkanes.

The present invention can be put into practice in various ways, depending in particular on the way in which the operation in which the catalyst is brought into contact

with the agent which forms hydrogen"in situ", is carried out, in particular if it is carried out either in the presence or in the absence of the starting alkane (s) used in the manufacture of alkanes. It can also depend on the nature of the agent, in particular whether the agent is provided in the gaseous, liquid or solid form.

More particularly, when the operation in which the catalyst is brought into contact or activated with the agent which forms hydrogen"in situ", is carried out in the absence of the starting alkane (s) used in particular in the manufacture of alkanes, it is then carried out separately from the operation in which the catalyst is brought into contact with the starting alkane (s). In this case, the two contacting operations of the catalyst can be carried out in at least two separate zones: in particular a reaction zone, where the manufacture of alkanes is carried out in particular by bringing the catalyst into contact essentially with the starting alkane (s), and an activation zone, where in particular the catalyst is brought into contact essentially with the agent. These two separate zones can be connected to one another via one or more transfer zones capable in particular of transferring at least a portion of the catalyst from one zone to the other.

In the specific case where the agent which forms hydrogen"in situ"is methane, the activation of the catalyst by methane is preferably carried out in the absence of the starting alkane (s) used in particular in the manufacture of alkanes. This means in particular that the activation of the catalyst by methane is carried out, in this case, separately from the manufacture of alkanes. Thus, the present invention can have as subject-matter a process for the manufacture of alkanes comprising bringing at least one starting alkane into contact with a metal catalyst comprising at least one metal, Me, bonded to at least one hydrogen atom and/or to at least one hydrocarbon radical, characterized in that, during the manufacture of alkanes, the catalyst is brought into contact with an agent which forms hydrogen"in situ", which contacting operation is carried out in the absence of the starting alkane (s) when the agent is methane. The present invention can also, in this case, have as subject-matter a process for the activation of a metal catalyst intended to manufacture alkanes and comprising at least one metal, Me, bonded to at least one hydrogen atom and/or to at least one hydrocarbon radical, which process is characterized in that, during the manufacture of alkanes carried out by bringing the catalyst into contact with at least one starting alkane, the catalyst is brought into contact with an agent which forms hydrogen"in situ", which contacting operation is carried out in the absence of the starting alkane (s) when the agent is

methane.

More generally, the manufacture of alkanes and the activation of the catalyst can be effectively carried out separately in at least two separate zones and the process according to the invention can be implemented either batchwise or, preferably, continuously. Furthermore, the two separate zones can in particular be connected to one another via a first zone for transfer of the catalyst which connects the zone in which the catalyst is brought into contact or activated with the agent to the reaction zone for the manufacture of alkanes, and via a second zone for transfer of the catalyst which connects the reaction zone for the manufacture of alkanes to the zone in which the catalyst is brought into contact or activated with the agent. One of the two transfer zones or preferably both transfer zones can be operated either batchwise or, preferably, continuously, in particular when the two separate zones of the process are themselves operated continuously. At least one of the two transfer zones can comprise a pipe or an elevator chosen in particular from mechanical, hydraulic (using a non-aqueous liquid, in particular a hydrocarbon liquid, such as an alkane) or, preferably, pneumatic pipes and elevators. The transfer of the catalyst in a hydraulic or, preferably, pneumatic pipe or an elevator can be carried out by virtue of a carrier fluid, in particular a carrier liquid or, preferably, a carrier gas, chosen in particular from at least one of the liquid or gaseous constituents present in the zone where the transfer is carried out. Such a method has the advantage of facilitating the transfer of the catalyst and of improving the reliability and the uniformity of the process. At least one of the two transfer zones can be preceded by a zone in which the catalyst is partially or completely separated from the other liquid or gaseous constituent (s) entrained with the catalyst out of the zone from where the catalyst originates. The other constituent (s) thus entrained and separated from the catalyst are preferably returned to the zone from where the catalyst originates. This method exhibits the advantage of being able to carry out the manufacture of the alkanes and the activation of the catalyst in an independent way, without in particular causing disruptions in one or the other of the two zones. In addition, it makes it possible to increase the output of the process.

The two separate zones for the manufacture of alkanes and for the activation of the catalyst can also be implemented according to other alternative forms, in particular when these zones are connected to one another via two transfer zones such as those described above. Thus, according to one alternative form, the manufacture of alkanes

can be carried out in a first zone in the absence of the agent which forms hydrogen"in situ", in particular by bringing the catalyst into contact with one or more starting alkanes comprising in particular at least two carbon atoms, while the operation in which the catalyst is brought into contact or activated with the agent which forms hydrogen"in situ", is carried out in a second separate zone optionally in the presence of one or more starting alkanes, identical to or different from those used in the first zone and comprising in particular at least one carbon atom, and while at least a portion of the catalyst is simultaneously transferred from one zone to the other.

According to another alternative form, the operation in which the catalyst is brought into contact or activated with the agent which forms hydrogen"in situ", chosen in particular to be other than methane, can be carried out in a first zone in the absence of alkane, while the manufacture of alkanes is carried out in a second separate zone in the presence of the agent which forms hydrogen"in situ", by bringing the catalyst into contact with one or more starting alkanes comprising in particular at least one carbon atom, and while at least a portion of the catalyst is simultaneously transferred from one zone to the other. One or other of these alternative forms can advantageously be carried out continuously.

The two separate zones of the process can be implemented in various ways. In particular, the manufacture of alkanes, carried out by bringing the catalyst into contact with the starting alkane (s), can be carried out either in a liquid-phase reaction zone or in a gas-phase reaction zone. In the first case, the liquid-phase reaction zone can contain a liquid phase essentially comprising the starting alkane (s), in particular in the liquid state under the conditions of the contacting operation, and/or one or more liquid inert agents.

The liquid phase can preferably be a liquid suspension comprising solid particles in particular which essentially comprise the catalyst in a solid form, preferably in a pulverulent or granular form. The liquid-phase reaction zone can comprise a liquid- phase reactor or loop, in particular a reactor or loop for a liquid-phase suspension, preferably equipped with one or more means chosen from stirring means, in particular for a suspension, or means for heat exchange, for heating and/or for cooling, for self- refrigeration, for condensation, for circulation, for recycling and for separation of the products charged and/or manufactured, in particular the gaseous, liquid and solid products, and for isolation and for recovery of the products manufactured.

The manufacture of alkanes can also be carried out in a gas-phase reaction zone

which can contain a gas phase essentially comprising the starting alkane (s), in particular in the gas state under the conditions of the operation of bringing into contact with the catalyst, and optionally one or more inert gases, such as nitrogen, helium or argon. In this case, the gas-phase reaction zone can comprise a gas-phase reactor or loop chosen in particular from fluidized bed reactors and/or reactors with a mechanically stirred bed, stationary bed reactors and circulating bed reactors, it being possible for the bed essentially to comprise the catalyst, in particular in a solid form, preferably in a pulverulent or granular form. The gas-phase reactor can be equipped with one or more means chosen from means for heat exchange, for heating and/or for cooling, for condensation, for stirring, for circulation, for recycling and for separation of the products used and/or manufactured, in particular the gaseous, solid and optionally liquid products, and for isolation and for recovery of the products manufactured.

Thus, the manufacture of alkanes can be carried out in a reaction zone, in particular a liquid-phase or, preferably, gas-phase reaction zone, such as described above. In this case, the process according to the invention can comprise the following stages, in particular carried out continuously: (a) the starting alkane (s) is (are) introduced into the reaction zone, (b) the starting alkane (s) is (are) brought into contact with the catalyst, in particular present in or introduced into the said zone, (c) a portion of the alkanes produced, entraining with them a portion of the unreacted starting alkane (s), is withdrawn out of the said zone, (d) the portion of alkanes produced is partially or completely separated from the portion of the unreacted starting alkane (s), and (e) the portion thus separated of the unreacted starting alkane (s) is preferably returned to the said zone, which portion is thus in particular brought back into contact with the catalyst.

The operation in which the catalyst is brought into contact or activated with the agent which forms hydrogen"in situ", can be carried out in a liquid-phase or gas-phase activation zone. In the case of a liquid-phase activation zone, the latter can contain a liquid phase which essentially can comprise at least one liquid inert agent. The liquid phase can preferably be a suspension comprising solid particles in particular which essentially comprise the catalyst in a solid form, preferably in a pulverulent or granular form, and optionally the agent which forms hydrogen"in situ", in a solid form, in particular when the latter is chosen from agents capable of releasing hydrogen, such as metal hydrides. The liquid phase can comprise, dissolved in it, at least a portion of the agent, in particular in a gaseous form, such as methane. It can also comprise, above it

and in equilibrium with it, a gas phase comprising in particular the agent in a gaseous form, such as methane. The liquid-phase activation zone can comprise a liquid-phase reactor or loop, in particular a reactor or loop for a liquid-phase suspension, equipped in particular with one or more means chosen from stirring means, in particular for a suspension, or means for heating and/or for cooling, for self-refrigeration, for condensation, for circulation, for recycling and for separation of the products used, manufactured and/or activated, in particular the gaseous, liquid and solid products, and for isolation and for recovery of the products manufactured and/or activated.

It is also possible to carry out the operation in which the catalyst is brought into contact or activated with the agent which forms hydrogen"in situ", in a gas-phase activation zone which can contain a gas phase essentially comprising the agent, in a gaseous form, such as methane, and/or one or more inert gases, such as nitrogen, helium or argon. The gas-phase activation zone can comprise in particular a gas-phase reactor or loop chosen in particular from fluidized bed reactors and/or reactors with a mechanically stirred bed, stationary bed reactors and circulating bed reactors, it being possible for the bed essentially to comprise the catalyst, in particular in a solid form, preferably in a pulverulent or granular form, and optionally the agent which forms hydrogen"in situ", in a solid form, in particular when the latter is chosen from agents capable of releasing hydrogen, such as metal hydrides. The gas-phase reactor is equipped with one or more means chosen from means for heat exchange, for heating and/or for cooling, for condensation, for circulation, for recycling and for separation of the products used, manufactured and/or activated, in particular the gaseous, solid and optionally liquid products, and for isolation and for recovery of the products manufactured and/or activated.

Thus, the activation can advantageously be carried out in a gas-phase activation zone, such as described above, and in particular continuously. In this case, the process according to the invention can comprise the following stages, preferably carried out continuously: (a) the catalyst is introduced into a gas-phase activation zone through which passes an essentially gaseous stream comprising the agent which forms hydrogen "in situ", in a gaseous form, and optionally one or more inert gases, so as to bring the catalyst into contact or to activate with the agent, the stream preferably being recycled in the said zone, and the catalyst thus introduced forming in particular a bed, especially a fluidized bed, through which passes the said stream, (b) a portion of the catalyst thus

activated is withdrawn and recovered out of the said zone, entraining with it a portion of the agent and/or of the hydrogen produced"in situ", (c) the portion thus withdrawn and recovered of the catalyst is optionally partially or completely separated from the portion, withdrawn and recovered, of the agent and/or of the hydrogen produced"in situ"thus entrained, and (d) the portion, thus separated, of the agent and/or of the hydrogen produced"in situ"is preferably returned to the said zone, which portion is thus in particular brought back into contact with the catalyst.

When the operation in which the catalyst is brought into contact or activated with the agent which forms hydrogen"in situ", is carried out in the presence of the starting alkane (s) used in particular in the manufacture of alkanes, the operations in which the catalyst is brought into contact with the agent and with the starting alkane (s) can then be carried out in a single zone. Thus, the manufacture of alkanes and the activation of the catalyst can be carried out together and simultaneously in a single zone, and preferably continuously. The single zone can be either a liquid-phase zone or a gas-phase zone.

In the case of a single liquid-phase zone, the latter can contain a liquid phase which essentially can comprise the starting alkane (s) and optionally one or more liquid inert agents. The liquid phase can preferably be a suspension comprising solid particles which essentially can comprise the catalyst especially in a solid form, preferably in a pulverulent or granular form, and optionally the agent which forms hydrogen"in situ", in a solid form, in particular when the latter is chosen from agents capable of releasing hydrogen, such as metal hydrides. The liquid phase can comprise, dissolved in it, a gas phase comprising in particular the agent which forms hydrogen"in situ", in a gaseous form, chosen in particular other than methane. The gas phase can also comprise, above it and in equilibrium with it, a gas phase comprising in particular the agent in a gaseous form, chosen in particular other than methane. The single liquid-phase zone can comprise a liquid-phase reactor or loop, preferably a reactor or loop for a liquid-phase suspension, such as described above, optionally equipped with one or more means chosen from stirring means, in particular for a suspension, or means for heat exchange, for heating and/or for cooling, for self-refrigeration, for condensation, for circulation, for recycling and for separation of the products used, manufactured and/or activated, in particular the gaseous, liquid and solid products, and for isolation and for recovery of the products manufactured and/or activated.

In the case of a single gas-phase zone, the latter can contain a gas phase which essentially can comprise the starting alkane (s), optionally the agent which forms hydrogen"in situ", in a gaseous form, preferably chosen other than methane, and optionally one or more inert gases, such as nitrogen, helium or argon. The single gas- phase zone can comprise a gas-phase reactor or loop preferably chosen from fluidized bed reactors and/or reactors with a mechanically stirred bed, stationary bed reactors and circulating bed reactors, it being possible for the bed essentially to comprise the catalyst especially in a solid form, preferably in a pulverulent or granular form, and optionally the agent which forms hydrogen"in situ", in a solid form, in particular when the latter is chosen from agents capable of releasing hydrogen, such as metal hydrides. The gas- phase reactor is preferably equipped with one or more means chosen from means for heat exchange, for heating and/or for cooling, for self-refrigeration, for condensation, for circulation, for recycling and for separation of the products used, manufactured and/or activated, in particular the gaseous, liquid and solid products, and for isolation and for recovery of the products manufactured and/or activated.

Thus, the process can be advantageously carried out in a single gas-phase zone, such as described above. It can comprise the following stages, preferably carried out continuously: (a) the starting alkane (s) and optionally one or more inert gases are introduced into a single gas-phase zone comprising the catalyst and the agent which forms hydrogen"in situ", both in solid forms capable of constituting in particular a bed, especially a fluidized bed, such that an essentially gaseous stream passes through the said zone, the stream preferably being recycled in the said zone, (b) a portion of the stream which has passed through the said zone and which comprises the alkanes produced is withdrawn out of the said zone, (c) the alkanes produced are partially or completely separated from the unreacted starting alkane (s), optionally from the hydrogen produced"in situ", and optionally from the inert gas or gases, and (d) the latter materials, thus separated from the alkanes produced, are optionally returned to the said zone and are thus in particular brought back into contact with the catalyst.

Figure 1 diagrammatically represents a device which makes it possible to implement the process according to the invention, in which device the manufacture of alkanes and the activation of the catalyst by an agent which forms hydrogen"in situ" (in particular an agent capable of releasing hydrogen, such as a transition metal hydride) are carried out simultaneously and preferably continuously in a single liquid-phase or,

preferably, gas-phase zone (1) containing a mixture (2) comprising the catalyst, in particular in a pulverulent or granular form, and the agent which forms hydrogen"in situ". The single zone (1) can comprise a liquid-phase reactor, in particular a reactor for a liquid-phase suspension, such as described above, equipped in particular with means for mechanical stirring and for heat exchange. Preferably, the single zone (1) can comprise a gas-phase reactor, in particular a fluidized bed reactor and/or a reactor with a mechanically stirred bed, or a stationary bed or circulating bed reactor, such as described above, equipped in particular with means for heat exchange and for circulation and/or for recycling of the products used and/or manufactured in the zone (1). The device can comprise one or more lines (3) and (4) for feeding the zone (1) with the starting alkane (s), which lines emerge directly or indirectly in the zone (1), in particular via a recycling line (11). These feed lines preferably feed the zone (1) continuously. The device can optionally comprise a line (5) for making up with the fresh catalyst and with the fresh agent which forms hydrogen"in situ"and a line (6) for making up with liquid or gaseous inert agent (s), in particular with one or more inert gases, such as nitrogen, helium or argon. The two make-up lines (5) and (6) can emerge in the zone (1) so as to feed this zone, preferably continuously, respectively with the fresh catalyst and with the fresh agent which forms hydrogen"in situ"and with the inert agent (s). The device can also comprise a line (7) for discharge of the catalyst and of the agent which forms hydrogen"in situ"and which exits from the zone (1), so as to discharge, preferably continuously, out of the zone a portion of the catalyst and of the said agent, in particular in excess, or optionally the spent or aged catalyst. A withdrawal line (8) can leave the zone (1), so as to withdraw, preferably continuously, out of this zone a mixture comprising at least a portion of the alkanes produced, of the unreacted starting alkane (s), optionally of the hydrogen produced"in situ"and optionally of the inert agent (s). The withdrawal line (8) can emerge directly or indirectly in a separating zone (9), so as to separate, partially or completely and preferably continuously, at least one of the constituents of the withdrawn mixture, in particular the alkanes produced, by separating them in particular from the unreacted starting alkane (s), optionally from the hydrogen produced"in situ"and optionally from the inert agent (s). The alkanes produced and thus separated can be recovered, in particular continuously, out of the separating zone (9) via a recovery line (10) exiting from this zone, while the other products separated in this zone, in particular the starting alkane (s), optionally the

hydrogen produced"in situ"and optionally the inert agent (s), can advantageously be returned, at least in part and in particular continuously, to the zone (1) via a recycling line (11). The separating zone (9) can comprise in particular one or more fractionating and/or condensing means.

Figure 2 diagrammatically represents an improved device in comparison with that illustrated in Figure 1 which makes it possible to implement the process according to the invention, preferably carried out continuously, and which comprises in particular a single gas-phase zone. The elements of the device according to Figure 2 which are identical to those of the device according to Figure 1, are given the same numbers. The device comprises a single gas-phase zone (1) which particularly comprises a gas-phase reactor (1') containing a bed (2'), preferably a fluidized bed, essentially comprising the catalyst and the agent which forms hydrogen"in situ". The reactor (1') is equipped in particular with a fluidization grid (12) and with a loop (13) for recycling an essentially gaseous stream comprising the starting alkane (s), the alkanes produced, optionally the hydrogen produced"in situ"and optionally one or more inert gases, such as nitrogen, helium or argon. The recycling loop (13) can leave the top of the reactor (1') and can return to the base of the latter. It can comprise a compressor (14) intended in particular to circulate, preferably continuously, the gas stream in the loop (13) and through the reactor (1') according to an in particular upward stream, in order to keep in particular the bed (2') in the fluidized state, and a heat exchanger (15) intended in particular to control and to maintain the temperature in the reactor (1'), in particular the temperature of the bed (2'), at a predetermined value. The device can comprise one or more lines (3) and (4) for feeding the reactor (1') with the starting alkane (s) and optionally a line (6) for making up with one or more inert gases. These feed lines can emerge in the recycling loop (13) of the reactor (1') and can preferably feed the reactor (1') continuously. The reactor (1') can. be equipped with a line (5) for making up with the fresh catalyst and with the fresh agent which forms hydrogen"in situ", which line can emerge in the reactor (1'), and with a line (7) for discharge of the catalyst and of the said agent, in particular in excess, or optionally the spent or aged catalyst and/or said agent, which line exits from the reactor (1'). A withdrawal line (8) can leave the recycling loop (13) so as to withdraw, in particular continuously, out of the reactor (1') and of the loop (13) a portion of the gas stream in the form of a mixture comprising the alkanes produced, the unreacted starting alkane (s), optionally the hydrogen produced

"in situ"and optionally the inert gas (es). The withdrawal line (8) can emerge directly or indirectly in a separating zone (9), which as mentioned above, so as to separate, partially or completely and preferably continuously, at least one of the constituents of the withdrawn mixture, in particular the alkanes produced, by separating them in particular from the starting alkane (s), optionally from the hydrogen produced"in'situ" and optionally from the inert gas (es). The alkanes produced and thus separated can be recovered, in particular continuously, out of the separating zone (9) via a recovery line (10) exiting from this zone, while the other products separated can be returned, at least in part and preferably continuously, to the recycling loop (13) via a recycling line (11).

Figure 3 diagrammatically represents a device which makes it possible to implement the process of the invention, in which device the manufacture of alkanes and the activation of the catalyst by the agent which forms hydrogen"in situ" (in particular an agent capable of forming hydrogen by a chemical reaction, such as methane) take place simultaneously and preferably continuously in two separate zones. The device comprises a liquid-phase or, preferably, gas-phase reaction zone (1) containing in particular the catalyst (2), preferably in a pulverulent or granular form, and preferably operating continuously. The reaction zone (1) can comprise a liquid-phase reactor or a gas-phase reactor, such as described above, optionally equipped with means for heat exchange, for stirring, for circulation or for recycling the products used and/or manufactured in the zone (1) such as those described above. The device can comprise a line (3) for feeding the zone (1) with the starting alkane (s) and optionally a line (6) for making up with liquid or gaseous inert agent (s), in particular with inert gas (es), such as nitrogen, helium or argon. The feed line (3) and the make-up line (6) can emerge directly or indirectly in the zone (1), for example via a recycling line (11), and can preferably feed the zone (1) continuously or can make up this zone with these constituents. The device can additionally comprise a withdrawal line (8) which can leave the zone (1), so as to withdraw, in particular continuously, out of the zone (1) a mixture comprising a portion of the alkanes produced, of the unreacted starting alkane (s) and optionally of the inert agent (s). The withdrawal line (8) can emerge directly or indirectly in a separating zone (9) providing in particular separating means such as those mentioned above. The separating zone (9) can operate so as to separate, partially or completely and preferably continuously, at least one of the constituents of the withdrawn mixture, in particular the alkanes produced, by separating them in

particular from the unreacted starting alkane (s) and optionally from the inert agent (s).

The alkanes produced and thus separated can be recovered in particular continuously, out of the separating zone (9) by a recovery line (10) exiting from this zone, while the other products separated in this zone, in particular the unreacted starting alkane (s) and optionally the inert agent (s), can be returned at least in part and preferably continuously, directly or indirectly, to the zone (1) by a recycling line (11).

A line (16) for discharge of a mixture comprising at least a portion of the catalyst, preferably in a pulverulent or granular form, entraining with it a portion of the alkanes produced, of the unreacted starting alkane (s) and optionally of the inert agent (s), can exit from the reaction zone (1). The discharge line (16) can be a pipe for mechanical or pneumatic transportation or in particular a mechanical or pneumatic elevator. The pipe or the elevator is particularly intended to transport from one point to another the catalyst in particular in a pulverulent form. The discharge line (16) can preferably operate continuously and emerge in a zone (17) for separation of the catalyst. The separating zone (17) can be in particular a phase separator, such as a solid/gas, solid/liquid or solid/liquid/gas separator, a cyclone separator or a separator by settling.

The separating zone (17) can operate so as to separate, partially or completely and preferably continuously, the catalyst from at least one of the constituents of the mixture discharged from the discharge line (16), in particular the alkanes produced, the unreacted starting alkane (s) and optionally the inert agent (s). A line (18) for transfer of the catalyst thus separated and a line (19) for returning the other product (s) separated can exit from the separating zone (17). The return line (19) can preferably operate continuously and emerge directly or indirectly in the reaction zone (1), in particular via the feed line (3) and the recycling line (11). The transfer line (18) can be a pipe for mechanical, hydraulic or pneumatic transportation or, in particular, a mechanical, hydraulic or pneumatic elevator, and can preferably operate continuously.

The transfer line (18) can communicate with a zone (20) for the activation of the catalyst, in particular a liquid-phase or, preferably, gas-phase activation zone, preferably operating continuously. The activation zone (20) can comprise a liquid-phase or, preferably, gas-phase reactor, such as described above, optionally equipped with means for heat exchange, for stirring, for circulation or for recycling of the products used and/or manufactured in this zone, such as the means mentioned above. A line (4) for feeding with the agent which forms hydrogen"in situ" (such as methane) can emerge in

the activation zone (20) and can preferably feed the zone (20) continuously. A line (6) for making up with the inert agent (s) can also emerge directly or indirectly in the activation zone (20), for example via the feed line (4), and can operate continuously.

The inert agent (s) feeding the activation zone (20) can be identical to or different from those introduced in the reaction zone (1).

A line (21) for recovery of a mixture comprising in particular the unreacted agent which forms hydrogen"in situ" (such as methane), the hydrogen and at least one other alkane, such as ethane and/or its higher homologues, produced"in situ"by the reaction of the activation of the catalyst by the said agent, can optionally exit from the activation zone (20). The recovery line (21) can preferably operate continuously and emerge in a separating zone (22) in particular a separating zone by fractionation, condensation or settling. The separating zone (22) can operate so as to separate and to recover, preferably continuously, the other alkane (s) from the mixture, in particular ethane and/or its higher homologues, and to return it or them by a return line (23), directly or indirectly and preferably continuously, to the reaction zone (1), for example via the feed line (3). The other product (s) separated in the separating zone (22), in particular the agent which forms hydrogen"in situ" (such as methane), can advantageously be returned, at least in part and preferably continuously, directly or indirectly by a line (24) to the activation zone (20), for example via the feed line (4), it being possible for the other part to be discharged to the outside by a line (25). A line (26) for withdrawal of a mixture comprising at least a portion of the activated catalyst, entraining with it a portion of the unreacted agent which forms hydrogen"in situ" (such as methane), of the hydrogen and of other alkane (s) produced"in situ", and optionally of the inert agent (s) can exit from the activation zone (20). The withdrawal line (26) can be a pipe for mechanical or pneumatic transportation or, in particular, a mechanical or pneumatic elevator, and can in particular operate continuously.

The withdrawal line (26) can emerge in a separating zone (27) which can be a phase separator, such as a solid/gas, solid/liquid or solid/liquid/gas separator, in particular a cyclone separator or a separator by settling. The separating zone (27) can operate so as to separate, partially or completely and preferably continuously, the activated catalyst from the mixture withdrawn from the activation zone (20) and to return, in particular continuously, the activated and thus separated catalyst to the reaction zone (1) by virtue of a recycling line (28) which can be a pipe for mechanical,

hydraulic or pneumatic transportation or, in particular, a mechanical, hydraulic or pneumatic elevator. A line (29) for returning the other product (s) separated, which can be returned, directly or indirectly and preferably continuously, to the activation zone (20), for example via the feed line (4), can exit from the separating zone (27). The reaction zone (1) can also be equipped with a line (5) for making up with the fresh catalyst which can emerge directly or indirectly in the zone (1), in particular via the recycling line (28), and with a line (7) for discharge of the catalyst, in particular the excess or optionally spent or aged catalyst, which can leave the reaction zone (1).

A device as illustrated in Figure 3 exhibits the advantage of employing a zone (1) for the manufacture of alkanes and a zone (20) for the activation of the catalyst which can operate simultaneously with a high output and in an independent way with respect to one another, in particular without the liquid or gas phase of one of the zones being disturbed or contaminated by one of the other.

Figure 4 diagrammatically represents an improved device in comparison with that illustrated in Figure 3 which makes it possible to implement the process according to the invention, preferably carried out continuously, and which comprises in particular two separate gas-phase zones, one intended to manufacture alkanes and the other intended to activate the catalyst, operating in particular in an independent way with respect to one another. The elements of the device according to Figure 4 which are identical to those of the device according to Figure 3, are given the same numbers. The device comprises a gas-phase reaction zone (1) which particularly can comprise a gas- phase reactor (1') preferably operating continuously and containing a bed, preferably a fluidized bed, essentially comprising the catalyst (2). The reactor (1') is equipped in particular with a fluidization grid (12) and with a loop (13) for recycling an essentially gaseous stream comprising the starting alkane (s), the alkanes produced and optionally one or more inert gases, such as nitrogen, helium or argon. The recycling loop (13) can leave the reactor (1') and can return to the base of the latter. It can comprise a compressor (14) intended in particular to circulate, in particular continuously, the gaseous stream in the loop (13) and through the reactor (1') according to an in particular upward stream, in order to maintain in particular the bed in the fluidized state, and a heat exchanger (15) intended in particular to control and to maintain the temperature of the reactor, in particular the temperature of the bed, at a predetermined value. The device can comprise a line (3) for feeding the reactor (1') with the starting alkane (s) and

optionally a line (6) for feeding the reactor (1') with the inert gas (es). These feed lines can in particular operate continuously and emerge in the recycling loop (13) of the reactor (1'). The reactor (1') can be equipped with a line (5) for making up with the fresh catalyst which can emerge directly or indirectly in the reactor (1') and with a line (7) for discharge of the catalyst, in particular the excess or optionally spent or aged catalyst, which can exit from the reactor (1'). A withdrawal line (8) can leave the recycling loop (13) so as to withdraw out of the reactor (1') and of the loop (13), in particular continuously, a portion of the gas stream in the form of a mixture comprising the alkanes produced, the unreacted starting alkane (s) and optionally the inert gas (es).

The withdrawal line (8) can emerge directly or indirectly in a separating zone (9) such as mentioned above, so as to separate, partially or completely and preferably continuously, at least one of the constituents of the withdrawn mixture, in particular the alkanes produced, by separating them in particular from the starting alkane (s) and optionally from the inert gas (es). The alkanes produced and thus separated can be recovered out of the separating zone (9), in particular continuously, via a recovery line (10) exiting from this zone, while the other products separated can advantageously be returned, at least in part and preferably continuously, to the recycling loop (13) by a recycling line (11).

A line (16) for discharge of an essentially solid/gas mixture comprising at least a portion of the catalyst in particular in a pulverulent or granular form, entraining with it a portion of the alkanes produced, of the unreacted starting alkane (s), and optionally of the inert gas (es), can exit from the reactor (1'). The discharge line (16) can be a pipe for mechanical transportation or a mechanical elevator or, preferably, a pipe for pneumatic transportation or a pneumatic elevator, and can preferably operate continuously. It can emerge in the zone (17) for separation of the catalyst which can be a phase separator, such as a solid/gas, solid/liquid or solid/liquid/gas separator, a cyclone separator or a separator by settling. The separating zone (17) can operate so as to separate, partially or completely and preferably continuously, the catalyst from at least one of the constituents of the mixture discharged via the discharge line (16), in particular the gaseous constituents or optionally the liquid constituents of this mixture, such as the alkanes produced, the unreacted starting alkane (s), and optionally the inert gas (es). A line (18) for transfer of the catalyst thus separated and a line (19) for returning the other product (s) separated in this zone, in particular a mixture comprising the alkanes

produced, the unreacted starting alkane (s), and optionally the inert gas (es), can exit from the separating zone (17). The return line (19) can preferably operate continuously and emerge directly or indirectly in the reactor (1'), in particular via the feed line (3) and/or the recycling loop (13). The transfer line (18) can be a pipe for mechanical transportation or a mechanical elevator or, preferably, a pipe for pneumatic transportation or pneumatic elevator, and can preferably operate continuously.

The transfer line (18) can communicate with a zone (20) for the activation of the catalyst, preferably a gas-phase activation zone which operates in particular continuously. The activation zone (20) can comprise the gas-phase reactor (20') containing a bed (30), preferably a fluidized bed, essentially comprising the catalyst in a solid form. The gas-phase reactor (20') can be equipped in particular with a fluidization grid (31) and with a loop (32) for recycling a gas stream essentially comprising the agent which forms hydrogen"in situ" (such as methane), optionally the hydrogen produced"in situ", the other alkane (s) produced"in situ"and one or more inert gases, such as nitrogen, helium or argon. The recycling loop (32) can leave the top of the reactor (20') and can return to the base of the latter. It can comprise a compressor (33) intended in particular to circulate, preferably continuously, the gas stream in the loop (32) and through the reactor (20') according to an in particular upward stream, in order to keep in particular the bed (30) in the fluidized state, and a heat exchanger (34) intended in particular to control and maintain the temperature of the reactor (20'), in particular the temperature of the bed (30) at a predetermined value. A line (4) for feeding with the agent which forms hydrogen"in situ" (such as methane) can preferably operate continuously and emerge directly or indirectly in the reactor (20'), in particular via the recycling loop (32). A line (6') for feeding with the inert gas (es) can optionally operate, in particular continuously and emerge directly or indirectly in the reactor (20'), in particular via the feed line (4) and/or the recycling loop (32). The inert gas (es) feeding the reactor (20') can be identical to or different from those introduced into the reactor (1').

A line (35) for diverting the gas stream circulating through the reactor (20') and the loop (32) can advantageously exit from the recycling loop (32). The diverting line (35) can preferably operate continuously and emerge in the transfer line (18), in order in particular to facilitate the transportation of the catalyst withdrawn from the separating zone (17) and its introduction into the reactor (20'). The advantage of such a method

results from the use of a carrier gas in the transfer line (18) in the form of a gas stream which is identical to that circulating through the reactor (20'). This makes it possible to improve the operation at the same time of the transfer line (18) and of the reactor (20').

A line (21) for recovery of an essentially gaseous mixture comprising the unreacted agent which forms hydrogen"in situ" (such as methane), optionally the hydrogen produced"in situ"and at least one other alkane, such as ethane and/or its higher homologues, produced"in situ"by the reaction for the activation of the catalyst, can optionally exit from the recycling loop (32). The recovery line (21) can preferably operate continuously and emerge in a separating zone (22), in particular a separating zone by fractionation, condensation or settling. The separating zone (22) can operate so as to separate and to recover, preferably continuously, the other alkane (s) from the mixture, in particular ethane and/or its higher homologues, and to return it or them, preferably continuously, by a return line (23), directly or indirectly to the reactor (1'), in particular via the feed line (3) and/or the recycling loop (13). The other product (s) separated in the separating zone (22), in particular the agent which forms hydrogen"in situ" (such as methane) and optionally the hydrogen produced"in situ", can advantageously be returned at least in part, directly or indirectly and preferably continuously, by a line (24) to the reactor (20'), in particular via the recycling loop (32), it being possible for another part to be discharged to the outside by a line (25). Such a method makes it possible to improve the output of the process.

A line (26) for withdrawal of an essentially solid/gas mixture comprising a portion of the activated catalyst, entraining with it the unreacted agent which forms hydrogen"in situ" (such as methane), optionally the hydrogen and the other alkane (s) produced"in situ", and optionally the inert gas (es), can exit from the reactor (20'). The withdrawal line can be a pipe for mechanical transportation or a mechanical elevator or, preferably, a pipe for pneumatic transportation or a pneumatic elevator, and can in particular operate continuously.

The withdrawal line (26) can emerge in a separating zone (27) which can be a phase separator, such as a solid/gas separator, a cyclone separator or a separator by settling. The separating zone (27) can operate so as to separate, partially or completely and preferably continuously, the activated catalyst from the mixture withdrawn from the reactor (20') and to return the catalyst, thus activated and separated, preferably continuously, to the reactor (1') by virtue of a recycling line (28). The line (28) can be a

pipe for mechanical transportation or a mechanical elevator or, preferably, a pipe for pneumatic transportation or a pneumatic elevator. Thus, the catalyst activated in the reactor (20') can be continuously transported to and recycled in the reactor (1') where the alkanes are manufactured. In order to facilitate the transportation of the activated catalyst to the reactor (1') and to improve the operation of this reactor, a line (36) for diverting the gas stream circulating through the reactor (1') can leave the recycling loop (13), can emerge in the recycling line (28) and can preferably operate continuously.

This method makes it possible advantageously to use a carrier gas in the recycling line (28) in the form of a gas stream identical to that circulating in the reactor (1') and thus to be able independently to manufacture the alkanes and to activate the catalyst.

Furthermore, the line (5) for making up with the fresh catalyst can emerge indirectly in the reactor (1') via the recycling line (28) in particular when the diverting line (36) emerges in the line (28).

A line (29) for returning the other product (s) separated in this zone, in particular the unreacted agent which forms hydrogen"in situ" (such as methane), optionally the hydrogen and other alkane (s) produced"in situ", and optionally the inert gas (es), which can be returned directly or indirectly and preferably continuously to the reactor (20'), in particular via the recycling loop (32), can exit from the separating zone (27). Such a method makes it possible to improve the output of the activation of the catalyst.

The catalyst used according to the present invention provides at least one metal, Me, atom bonded to at least one hydrogen atom and/or to at least one hydrocarbon radical. It is preferably chosen from metal catalysts supported on and in particular grafted to a solid support.

The term"metal catalyst supported on and grafted to a solid support"is generally understood to mean a metal catalyst or compound providing a solid support and at least one metal, Me, which is (chemically) attached to the support, in particular by at least one single or multiple bond, and in particular which is bonded directly to at least one of the essential elements (or constituents) of the solid support.

The metal, Me, present in the catalyst can be at least one metal chosen from the lanthanides, the actinides and the metals from Groups 2 to 12, preferably from Groups 3 to 12, in particular from the transition metals from Groups 3 to 11, and in particular from Groups 3 to 10, of the Periodic Table of the Elements. The metal, Me, can be in particular at least one metal chosen from scandium, yttrium, lanthanum, titanium,

zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, rhenium, iron, ruthenium, cobalt, rhodium, iridium, nickel, palladium, platinum, cerium and neodymium. It can preferably be chosen from yttrium, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, ruthenium, rhodium and platinum and more particularly from yttrium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, ruthenium, rhodium and platinum.

The catalyst can be chosen from metal catalysts or compounds supported on and grafted to a solid support, comprising a solid support and one or more metals, Me, which are identical or different and which are in particular (chemically) attached to the support, especially by single or multiple bonds. In the case of the metal, Me, grafted to a support is bonded to at least one hydrogen atom, the catalyst can be chosen from supported and grafted metal catalysts or compounds comprising a solid support to which is grafted at least one metal hydride, in particular a hydride of the metal Me.

In the case where the metal, Me, grafted to a support is bonded to at least one hydrocarbon radical, the catalyst can be chosen from supported and grafted metal catalysts or compounds comprising a solid support to which is grafted at least one organometallic compound, in particular an organometallic compound of the metal Me.

The catalyst can advantageously be chosen from metal hydrides and organometallic compounds of the metal Me, preferably supported on and grafted to a solid support.

The catalyst can be advantageously chosen from supported and grafted metal catalysts or compounds comprising a solid support to which are grafted at least two types of metal Me, one in a form (A) of a metal compound where the metal, Me, is bonded to at least one hydrogen atom and/or to at least one hydrocarbon radical, and the other in a form (B) of a metal compound where the metal, Me, is bonded solely to the support and optionally to at least one other element which is neither a hydrogen atom nor a hydrocarbon radical. In each of the forms (A) and (B), the catalyst can comprise one or more different metals, Me. The metal Me present in the form (A) can be identical to or different from that present in the form (B). When the forms (A) and (B) coexist in the catalyst, the degree of oxidation of the metals Me present in the form (A) can be identical to or different from that of the metals Me present in the form (B).

The solid support can be any solid support, preferably any solid inorganic support, in particular comprising essentially atoms M and X which are different from

one another and which are generally bonded to one another by single or multiple bonds, so as to form in particular the molecular structure of the solid support. The term "support comprising essentially atoms M and X"is generally understood to mean a support which comprises the atoms M and X as predominant constituents and which can additionally comprise one or more other atoms capable of modifying the structure of the support.

The atom M of the support can be at least one of the elements chosen from the lanthanides, the actinides and the elements from Groups 2 to 15 of the Periodic Table of the Elements. The atom M of the support can be identical to or different from the metal Me. The atom M can be at least one of the elements chosen in particular from magnesium, titanium, zirconium, cerium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, boron, aluminium, gallium, silicon, germanium, phosphorus and bismuth. The atom M of the support is preferably at least one of the elements chosen from the lanthanides, the actinides and the elements from Groups 2 to 6 and from Groups 13 to 15 of the Periodic Table of the Elements, in particular from silicon, aluminium and phosphorus.

The atom X of the support, which is different from the atom M, can be chosen from at least one of the elements from Groups 15 and 16 of the Periodic Table of the Elements, it being possible for the element to be alone or itself optionally bonded to another atom or to a group of atoms. In the case where the atom X of the support is chosen in particular from at least one of the elements from Group 15, it can optionally be bonded to another atom or to a group of atoms chosen, for example, from a hydrogen atom, a halogen atom, in particular a fluorine, chlorine or bromine atom, a saturated or unsaturated hydrocarbon radical, a hydroxyl group of formula (HO-), a hydrosulphide group of formula (HS-), alkoxide groups, thiolate groups, silylated (or silane) groups or organosilylated (or organosilane) groups. Preferably, the atom X of the support is at least one of the elements chosen from oxygen, sulphur and nitrogen and more particularly from oxygen and sulphur.

The atoms M and X, which generally represent the essential elements of the solid support, can in particular be bonded to one another via single or double bonds. In a preferred alternative form, the solid support can be chosen from oxides, sulphides and azides, in particular M, and mixtures of two or three oxides, sulphides and/or azides, and preferably from metal oxides, refractory oxides, molecular sieves, sulphated metal

oxides, sulphated refractory oxides, metal sulphides, refractory sulphides, sulphided metal oxides, sulphided refractory oxides and azides. More particularly, the support can be an oxide, in particular M, and can be chosen from simple or mixed oxides, in particular M, or mixtures of oxides, in particular M. The support can, for example, be chosen from metal oxides, refractory oxides and molecular sieves, in particular from silica, alumina, aluminosilicates, silicoaluminates, simple or modified by other metals, zeolites, clays, titanium oxide, cerium oxide, magnesium oxide, niobium oxide, tantalum oxide and zirconium oxide. The support can also be a metal oxide or a refractory oxide, optionally modified by an acid, and can optionally comprise in particular an atom M bonded to at least two atoms X which are different from one another, for example the oxygen atom and the sulphur atom. Thus, the solid support can be chosen from sulphated metal oxides and sulphated refractory oxides, for example a sulphated alumina or a sulphated zirconia. The support can also be chosen from metal sulphides, refractory sulphides, sulphided metal oxides and sulphided refractory oxides, for example a molybdenum sulphide, a tungsten sulphide or a sulphided alumina. The support can also be chosen from azides, in particular boron azides.

The essential constituents of the solid support are preferably the atoms M and X described above. In addition, the solid support has the advantage of generally exhibiting, at the surface, atoms X capable of forming part of the coordination sphere of the metal, Me, of the catalyst, in particular when the catalyst is chosen from metal catalysts or compounds supported on and grafted to a solid support. Thus, at the surface of the support, the atom X which is bonded to at least one metal atom, Me, can advantageously be additionally bonded to at least one atom M. The bonds between X and M and those between X and Me can be single or double bonds.

In the case of a metal catalyst supported on and grafted to a support, the metal, Me, present in particular in the form (A) can be bonded, on the one hand, to the support, in particular to at least one atom constituting the support, preferably the atom X of the support as described above, in particular by a single or double bond, and, on the other hand, to at least one hydrogen atom and/or to at least one hydrocarbon radical, in particular by a carbon-metal single, double or triple bond.

The catalyst, for example in the form (A) described above, can comprise at least one metal, Me, bonded to at least one hydrocarbon radical, R, which may be saturated or unsaturated, can have from 1 to 20, preferably from 1 to 10, carbon atoms and can be

chosen from alkyl, alkylidene or alkylidyne radicals, in particular Cl to Clo radicals, aryl radicals, in particular C6 to Clo radicals, and aralkyl, aralkylidene or aralkylidyne radicals, in particular C7 to C14 radicals. The metal, Me, can be bonded to the hydrocarbon radical, R, via one or more carbon-metal single, double or triple bonds. It can be a matter of a carbon-metal single bond, in particular of the s type: in this case, the hydrocarbon radical, R, can be an alkyl radical, in particular a linear or branched radical, for example a Cl to Clos preferably Cl, radical, or an aryl radical, for example the phenyl radical, or an aralkyl radical, for example the benzyl radical. The term"alkyl radical"is generally understood to mean a monovalent aliphatic radical resulting from the removal of a hydrogen atom from the molecule of an alkane or of an alkene or of an alkyne, for example the methyl, ethyl, propyl, neopentyl, allyl or ethynyl radical. The methyl radical is preferred.

It can also be a matter of a carbon-metal double bond, in particular of the p type: in this case, the hydrocarbon radical, R, can be an alkylidene radical, in particular a linear or branched radical, for example Cl to Clo, preferably Cl, radical, or an aralkylidene radical, for example a C7 to C14 radical. The term"alkylidene radical"is generally understood to mean a bivalent aliphatic radical originating from the removal of two hydrogen atoms from the same carbon of the molecule of an alkane or of an alkene or of an alkyne, for example the methylidene, ethylidene, propylidene, neopentylidene or allylidene radical. The methylidene radical is preferred. The term "aralkylidene radical"is generally understood to mean a bivalent aliphatic radical originating from the removal of two hydrogen atoms from the same carbon of an alkyl, alkenyl or alkynyl linking unit of an aromatic hydrocarbon.

It can also be a matter of a carbon-metal triple bond: in this case, the hydrocarbon radical, R, can be an alkylidyne radical, in particular a linear or branched radical, for example a Cl to Clo, preferably Cl, radical, or an aralkylidyne radical, for example a C7 to C14 radical. The term"alkylidyne radical"is generally understood to mean a trivalent aliphatic radical originating from the removal of three hydrogen atoms from the same carbon of the molecule of an alkane or of an alkene or of an alkyne, for example the methylidyne, ethylidyne, propylidyne, neopentylidyne or allylidyne radical.

The methylidyne radical is preferred. The term"aralkylidyne radical"is generally understood to mean a trivalent aliphatic radical originating from the removal of three hydrogen atoms from the same carbon of an alkyl, alkenyl or alkynyl linking unit of an

aromatic hydrocarbon.

The catalyst can advantageously be chosen from metal catalysts or compounds supported on and grafted to a solid support comprising the metal, Me, present in both forms (A) and (B). Such a catalyst has the advantage of exhibiting a very high catalytic activity in the manufacture of alkanes. The form (A) of the catalyst is that described above. In the form (B), the metal, Me, is preferably bonded solely to the support, in particular to one or more atoms constituting the essential elements of the support, in particular to one or more atoms X of the support such as are described above, for example by single or double bonds.

In the form (B), the metal, Me, can optionally be bonded, in addition to the support, to at least one other element which is neither a hydrogen atom nor a hydrocarbon radical. The other element bonded to the metal Me can, for example, be at least one of the elements from Groups 15 to 17 of the Periodic Table of the Elements, which element can be alone or itself bonded to at least one hydrogen atom and/or to at least one hydrocarbon radical and/or to at least one silylated (or silane) or organosilylated (or organosilane) group. In particular, the metal, Me, present in the form (B) can also be bonded, in addition to the support, to at least one atom of the elements chosen from oxygen, sulphur, nitrogen and halogens, in particular fluorine, chlorine or bromine. Thus, for example, the metal, Me, can be bonded, via a single bond, to one or more halogen atoms, in particular fluorine, chlorine or bromine. It can also be bonded, via a double bond, to one or more oxygen or sulphur atoms, in particular in the form of a metal oxide or sulphide. It can also be bonded, via a single bond, to at least one oxygen or sulphur atom itself bonded to a hydrogen atom or to a saturated or unsaturated hydrocarbon radical, in particular a Cl to C20, preferably Cl to CIO, radical, for example in the form of a hydroxide, of a hydrosulphide, of an alkoxide or of a thiolate. It can also be bonded, via a single bond, to a silylated or organosilylated group.

It can also be bonded, via a single bond, to an amido (or amide) group, for example of formulae (H2N-), (HRN-) or (RR'N-) in which R and R', which are identical or different, represent saturated or unsaturated hydrocarbon radicals, in particular Cl to C20, preferably Cl to Clo, radicals or silylated or organosilylated groups or else can be bonded, via a double bond, to an imido (or imide) group, for example of formula (HN =), or, via a triple bond, to a nitrido (or azide) group, for example of formula (N =).

It is preferable to use metal catalysts supported on or grafted to a solid support in

which the metal, Me, grafted to the support exists simultaneously in both forms (A) and (B), as these catalysts advantageously exhibit a very high catalytic activity in the manufacture of alkanes. This is in particular the case when, per 100 mol of the metal Me grafted to the support, the catalyst comprises: (a) from 5 to 95 mol, preferably from 10 to 90 mol, in particular from 20 to 90 mol, especially from 25 to 90 mol, or more particularly from 30 to 90 mol, of the metal Me in the form (A), and (b) from 95 to 5 mol, preferably from 90 to 10 mol, in particular from 80 to 10 mol, especially from 75 to 10 mol, or more particularly from 70 to 10 mol, of the metal Me in the form (B).

The catalysts described above can be prepared in various ways. A first process for the preparation of a metal catalyst supported on and grafted to a solid support can comprise the following stages: (a) an organometallic precursor (P) comprising the metal Me bonded to at least one hydrocarbon ligand is grafted to the solid support, and (b) the solid product resulting from stage (a) is treated with hydrogen or a reducing agent capable of forming a metal Me-hydrogen bond, preferably by hydrogenolysis of the hydrocarbon ligands, at a temperature in particular at most equal to the temperature T1 at which the catalyst is formed solely in the form (A) as defined above.

The temperature of stage (b) is chosen in particular so that it is at most equal to the temperature T1 where only the form (A) of the catalyst is formed, that is to say where only the metal hydride is formed. The temperature of stage (b) can in particular be chosen within a range from 50 to 160°C, preferably from 100 to 150°C. Stage (b) can take place under an absolute pressure of 10-3 to 10 MPa and for a period of time which can range from 1 to 24 hours, preferably from 5 to 20 hours.

A second process for the preparation of a catalyst can comprise the following stages: (a) an organometallic precursor (P) comprising the metal Me bonded to at least one hydrocarbon ligand is grafted to the solid support, and (b) the solid product resulting from stage (a) is treated with hydrogen or a reducing agent capable of forming a metal Me-hydrogen bond, preferably by hydrogenolysis of the hydrocarbon ligands, at a temperature greater than the

temperature T1 at which the catalyst is formed solely in the form (A) and less than the temperature T2 at which the catalyst is formed solely in the form (B), the forms (A) and (B) being those described above.

The temperature of stage (b) is chosen in particular so that it is greater than the temperature T1 where only the form (A) is formed. It can in particular be at least 10°C, preferably at least 20°C, in particular at least 30°C or even at least 50°C greater than the temperature T1. It is in addition chosen in particular so that it is less than the temperature T2 where only the form (B) is formed. It can in particular be at least 10°C, preferably at least 20°C, in particular at least 30°C or even 50°C less than the temperature T2. The temperature of stage (b) can, for example, be chosen within a range from 165°C to 450°C, preferably from 170 to 430°C, in particular from 180 to 390°C, in particular from 190 to 350°C or from 200 to 320°C. Stage (b) can take place under an absolute pressure of 10-3 to 10 MPa and for a period of time which can range from 1 to 24 hours, preferably from 5 to 20 hours.

A third process for the preparation of a catalyst can comprise the following stages: (a) an organometallic precursor (P) comprising the metal Me bonded to at least one hydrocarbon ligand is grafted to the solid support, then (b) the solid product resulting from stage (a) is treated with hydrogen or a reducing agent capable of forming a metal Me-hydrogen bond, preferably by complete hydrogenolysis of the hydrocarbon ligands, at a temperature in particular at most equal to the temperature T1 at which the catalyst is formed solely in the form (A) as defined above, so as to form a metal hydride in the form (A), and (c) the solid product resulting from stage (b) is heat treated, preferably in the presence of hydrogen or of a reducing agent, at a temperature greater than the temperature of stage (b) and less than the temperature T2 at which the catalyst is formed solely in the form (B) as defined above.

Stage (b) of the process can be carried out under the same conditions, in particular of temperature, as those of stage (b) of the first preparation process. Stage (c) can be carried out at a temperature, under a pressure and for a period of time equivalent to those described in stage (b) of the second preparation process.

A fourth process for the preparation of a catalyst can comprise the following stages:

(a) an organometallic precursor (P) comprising the metal Me bonded to at least one hydrocarbon ligand is grafted to the solid support comprising functional groups capable of grafting the precursor (P) by bringing the precursor (P) into contact with the solid support so as to graft the precursor (P) to the support by reaction of (P) with a portion of the functional groups of the support, preferably from 5 to 95% of the functional groups of the support, then (b) the solid product resulting from stage (a) is heat treated, preferably in the presence of hydrogen or of a reducing agent, at a temperature equal to or greater than the temperature T2 at which the catalyst is formed solely in the form. (B) as defined above, then (c) an organometallic precursor (P'), identical to or different from (P), comprising the metal Me bonded to at least one hydrocarbon ligand, the metal Me and the ligand being identical to or different from those of (P), is grafted to the solid product resulting from stage (b) by bringing the precursor (P') into contact with the solid product resulting from stage (b) so as to graft the precursor (P') to the support by reaction of (P') with the functional groups remaining in the support, and optionally (d) the solid product resulting from stage (c) is treated with hydrogen or a reducing agent capable of forming metal Me-hydrogen bonds, preferably by complete hydrogenolysis of the hydrocarbon ligands of the grafted precursor (P'), at a temperature in particular at most equal to the temperature T1 at which the catalyst is formed solely in the form (A) as defined above.

Stage (b) of the process can be carried out at a temperature such that most, preferably all, of the precursor (P) grafted to the support is converted to metal compound in the form (B). The temperature during stage (b) can be chosen within a range from 460°C, preferably from 480°C, in particular from 500°C, up to a temperature below the sintering temperature of the support. Stage (d) is optional and can be carried out at a temperature equivalent to that of stage (b) of the first preparation process.

A fifth process for the preparation of a catalyst can comprise the following stages: (a) an organometallic precursor is grafted to the solid support under the same conditions as in stage (a) of the preceding preparation process, then (b) the solid product resulting from stage (a) is treated under the

same conditions as in stage (b) of the preceding preparation process, then (c) the solid product resulting from stage (b) is brought into contact with at least one compound Y capable of reacting with the metal Me of the form (A) and/or (B), prepared above, the contacting operation preferably being followed by removal of the unreacted compound Y and/or by a heat treatment at a temperature below the sintering temperature of the support, then (d) an organometallic precursor (P'), identical to or different from (P), comprising the metal Me bonded to at least one hydrocarbon ligand, the metal Me and the ligand being identical to or different from those of (P), is grafted to the solid product resulting from stage (c) by bringing the precursor (P') into contact with the product resulting from stage (c) so as to graft the precursor (P') to the support by reaction of (P') with the functional groups remaining in the support, and optionally (e) the solid product resulting from stage (d) is treated with hydrogen or a reducing agent capable of forming metal Me-hydrogen bonds, preferably by complete hydrogenolysis of the hydrocarbon ligands of the grafted precursor (P'), at a temperature in particular at most equal to the temperature T1 at which the catalyst is formed solely in the form (A) as defined above.

Stage (b) of the process can be carried out at a temperature equivalent to that of stage (b) of the fourth preparation process. In stage (c), the compound Y can be chosen from molecular oxygen, water, hydrogen sulphide, ammonia, an alcohol, in particular a Cl to C20, preferably Cl to Clo, alcohol, a thiol, in particular a Cl to C20, preferably Cl to CIO, thiol, a primary or secondary Cl to C20, preferably Cl to Clo, amine, a molecular halogen, in particular molecular fluorine, chlorine or bromine, and a hydrogen halide, for example of formula HF, HC1 or HBr. The heat treatment optionally carried out at the end of stage (c) can be carried out at a temperature ranging from 25 to 500°C. Stage (e) is optional and can be carried out at a temperature equivalent to that of stage (b) of the first preparation process.

In the processes for the preparation of a supported and grafted metal catalyst such as are described above, the operation of grafting to a solid support employs at least one organometallic precursor (P) or (P') comprising the metal Me bonded to at least one hydrocarbon ligand. The precursor can correspond to the general formula: MeR'a (7)

in which Me has the same definition as above, R'represents one or more identical or different and saturated or unsaturated hydrocarbon ligands, in particular aliphatic or alicyclic ligands, in particular Cl to C20, preferably Cl to Clo, ligands, for example having the same definition as that given above for the hydrocarbon radical, R, of the metal catalyst, and a is an integer equal to the degree of oxidation of the metal Me. The radical R'can be chosen from alkyl, alkylidene, alkylidyne, aryl, aralkyl, aralkylidene and aralkylidyne radicals. The metal Me can be bonded to one or more carbons of the hydrocarbon ligands, R', in particular via carbon-metal single, double or triple bonds, such as those connecting the metal Me to the hydrocarbon radical, R, in the catalyst.

In the processes for the preparation of a supported and grafted metal catalyst such as are described above, the solid support is preferably subjected beforehand to a dehydration and/or dehydroxylation heat treatment, in particular at a temperature below the sintering temperature of the support, preferably at a temperature ranging from 200 to 1000°C, preferably from 300 to 800°C, for a period of time which can range from 1 to 48 hours, preferably from 5 to 24 hours. The temperature and the duration can be chosen so as to create and/or to allow to remain, in the support and at predetermined concentrations, functional groups capable of grafting by reaction the precursor (P) or (P'). Mention may be made, among functional groups known for the supports, of groups of formulae XH in which H represents a hydrogen atom and X corresponds to the same definition as given above for the support and in particular can represent an atom chosen from oxygen, sulphur and nitrogen. The most well known functional group is the hydroxyl group.

The grafting operation can generally be carried out by sublimation or by bringing the precursor into contact in a liquid medium or in solution. In the case of a sublimation, the precursor, used in the solid state, can be heated under vacuum and the temperature and pressure conditions which provide for its sublimation and its migration in the vapour state onto the support. The sublimation can be carried out at a temperature ranging from 20 to 300°C, in particular from 50 to 150°C, under vacuum.

A grafting can also be carried out by carrying out the contacting operation in a liquid medium or solution. In this case, the precursor can be dissolved in an organic solvent, such as pentane or ethyl ether, so as to form a homogeneous solution, and the support can subsequently be suspended in the solution comprising the precursor or by

any other method which provides for contact between the support and the precursor.

The contacting operation can be carried out at ambient temperature (20°C) or more generally at a temperature ranging from-80°C to +150°C, under an inert atmosphere, such as nitrogen. If only a portion of the precursor has become attached to the support, the excess can be removed by washing or reverse sublimation.

The following examples illustrate the present invention.

Example 1: preparation of a tantalum catalyst.

A tantalum catalyst supported on and grafted to silica was prepared in the following way.

In a first step, 5 g of a silica dehydrated and treated at 500°C beforehand and then 20 ml of an n-pentane solution comprising 800 mg (1. 72 millimol of tantalum) of tris (neopentyl) neopentylidenetantalum, used as precursor and corresponding to the general formula: Ta [-CH2-C (CH3) 3] 3 [=CH-C (CH3) 3] (8) were introduced under an argon atmosphere into a glass reactor. The precursor was grafted at 25°C to the silica, in particular by reaction with the hydroxyl groups of the silica. The excess precursor which had not reacted was removed by washing with n- pentane. The resulting solid compound, which constituted the organometallic compound grafted to the silica and which corresponded to the general formula: (Si-0) i. 35Ta [=CH-C (CH3) 3] [-CH2-C (CH3) 3] i. 65 (9) was then dried under vacuum.

In a second stage, the tantalum compound, thus supported on and grafted to the silica, was subsequently treated under an atmosphere of 80 kPa of hydrogen at a temperature of 150°C for 15 hours. By hydrogenolysis of the neopentyl and neopentylidene ligands, a tantalum catalyst supported on and grafted to silica was formed which comprised in particular a tantalum hydride grafted to the silica in a form corresponding to the following general formula: [ (silica support)-Si-0] 2-Ta-H (10)

Example 2: reaction for the metathesis of propane in the presence of a tantalum catalyst and separate contacting of the catalyst with methane.

Several successive reactions for the metathesis of propane were carried out under the same conditions and in the presence of the tantalum catalyst prepared in Example 1, except that, at the end of each metathesis reaction, the catalyst was recovered and was then subjected, on each occasion, to an operation of contacting with methane before being reused in the following reaction for the metathesis of propane.

Methane is an agent which forms hydrogen"in situ"capable of producing hydrogen by a chemical reaction in the presence of the catalyst prepared in Example 1: the reaction is a non-oxidative methane coupling reaction and results in the formation of hydrogen and ethane. In each reaction for the metathesis of propane, the initial rate (at time t=0 minute) and the final rate (after a reaction time of 8000 minutes) of propane consumption were measured. Thus, the initial rate of the metathesis reaction after each operation of contacting of the catalyst was compared with the final rate of the preceding metathesis reaction. It was thus possible to show that the catalyst had been effectively reactivated after each operation of activation of the catalyst with methane, and in particular that the catalyst activity was substantially sustained over time during the metathesis reaction which followed the contacting of the catalyst with methane.

The reaction for the metathesis of propane is written essentially according to the following equation: 2 C3Hg + C2H6 + C4H, o (11) Each reaction for the metathesis of propane was carried out under the following conditions. A reactor comprised 0.52 g of the tantalum catalyst prepared in Example 1 (comprising 5.33% by weight of tantalum) under an argon atmosphere and at ambient temperature (25°C). The reactor was filled with propane at atmospheric pressure and was then heated at 150°C under a continuous stream of propane at a constant flow rate of 1 ml/min (measured under standard conditions) at atmospheric pressure. This continuous stream ws maintained under these conditions, at 150°C and atmospheric pressure, for a period of time of 8000 minutes.

Each operation of contacting of the catalyst with methane was carried out under the following conditions. The tantalum catalyst was recovered in the reactor at the end

of a metathesis reaction, after having cooled the reactor to ambient temperature (25°C), having purged the reactor with argon and having subsequently filled the reactor with methane to an absolute pressure of 5 MPa. A continuous stream of methane passed through the reactor, thus comprising the catalyst, at a constant flow of 1 ml/min (measured under standard conditions) under an absolute pressure of 5 MPa. The reactor was heated to 250°C and was maintained at this temperature for 15 h. At the end of this period, the reactor was cooled to ambient temperature, was then decompressed and purged with argon, and. was filled with argon, so that the catalyst thus activated was ready for a new metathesis reaction.

It was observed that the reaction for the metathesis of propane thus carried out produced, on each occasion, essentially ethane and butane, and small amounts of methane and of Cs homologues. At each metathesis reaction, the initial rate and the final rate of reaction of the propane were measured and the rate of the catalyst deactivation was calculated. These measurements and calculations were carried out during a first metathesis reaction, then during a second metathesis reaction, preceded by a first activation, and during a third metathesis reaction, itself preceded by a second activation.

These measurements and calculations showed that the tantalum catalyst was reactivated (or regenerated) in the reaction for the metathesis of propane after each operation of activation of the catalyst with methane: after the first activation, the initial rate of the second reaction for the metathesis of propane was greater than the final rate of the first reaction for the metathesis of propane, and the rate of the catalyst deactivation was slower. It was the same after the second activation: the initial rate of the third reaction for the metathesis of propane was substantially greater than the final rate of the second reaction for the metathesis of propane, and the rate of the deactivation of the catalyst was slower.

Example 3: preparation of a tungsten catalyst.

A tungsten catalyst supported on and grafted to silica was prepared exactly as in Example 1, except that, in the first stage, instead of using a solution of tris (neopentyl) neopentylidenetantalum in n-pentane, use was made of a solution of tris (neopentyl) neopentylidynetungsten in n-pentane, corresponding to the general formula: W [-CH2-C (CH3) 313 [-C-C (CH3) 3] (12)

and that, in the second stage, instead of carrying out the hydrogenolysis at 250°C, it was carried out at 150°C. A tungsten catalyst supported on silica was thus obtained essentially in the form (A) of a tungsten hydride.

Example 4: reaction for the metathesis of propane in the presence of a tungsten catalyst and separate contacting of the catalyst with methane.

The same successive reactions for the metathesis of propane and the same operations for the contacting of the catalyst with methane were carried out as in Example 2, except that, instead of using the tantalum catalyst, the tungsten catalyst prepared in Example 3 was used.

Under these conditions, it was observed that the tungsten catalyst was reactivated in the reaction for the metathesis of propane after each operation of contacting of the catalyst with methane, and in particular that the rate of the deactivation of the catalyst was slower after each contacting of the catalyst with methane.

Example 5: reaction for the metathesis of propane in the presence of a tantalum catalyst with simultaneous contacting of the catalyst with a masnesium/nickel intermetallic hydride.

The reaction for the metathesis of propane was carried out under the following conditions. 0.52 g of the tantalum catalyst prepared in Example 1 (comprising 5.33% by weight of tantalum) and a magnesium/nickel intermetallic hydride in bulk form were introduced into a reactor at ambient temperature (25°C) under an argon atmosphere. The intermetallic hydride was a hydride of an alloy of magnesium and nickel (Mg2Ni) corresponding to the general formula: Mg2Ni-Mg2NiH4 and formed hydrogen"in situ"which had reversibly accumulated hydrogen and which was capable in particular of releasing the accumulated hydrogen. The reactor was subsequently filled with propane at atmospheric pressure. The reactor was subsequently heated at 150°C under a continuous stream of propane at a constant flow rate of 1 ml/min (measured under standard conditions) at atmospheric pressure. This continuous stream was maintained under these conditions, at 150°C at atmospheric pressure, for 8000 minutes.

It was observed that, under these conditions, the reaction for the metathesis of propane, which produced essentially ethane and butane, took place simultaneously with

a reaction for the activation of the tantalum catalyst. This was because the activity of the catalyst in the metathesis reaction was particularly sustained over time and was in particular greater than that in the same reaction carried out in the absence of the intermetallic hydride.

Example 6: reaction for the methane-olysis of propane in the presence of a tantalum catalyst with simultaneous contacting of the catalyst with a magnesium hydride.

A supported and grafted tantalum catalyst was prepared exactly as in Example 1, except that, in the second stage, instead of carrying out the hydrogenolysis at 150°C, it was carried out at 250°C. A tantalum catalyst supported on and grafted to silica was thus obtained, 72% of the tantalum of which was found in the form of a tantalum hydride corresponding to the general formula (10) as mentioned above.

A mixture of methane and propane in a molar ratio of methane to propane of 106/7X102 was passed continuously, according to a constant flow rate of 1.5 ml/min (measured under standard conditions), under a methane partial pressure of 5 MPa, through a reactor heated to 250°C and comprising 0.3 g of the tantalum catalyst thus prepared and a magnesium binary hydride in bulk form. The magnesium binary hydride was a metal hydride of the Mg-MgH2 type which formed hydrogen"in situ"which had reversibly accumulated a large amount of hydrogen and which was capable in particular of releasing the accumulated hydrogen.

It was observed that, under these conditions, the reaction for the methane-olysis of propane, which produced essentially ethane, took place simultaneously with a reaction for the activation of the tantalum catalyst. This was because the activity of the catalyst in the methane-olysis reaction was particularly sustained over time and was in particular greater than that in the same reaction carried out in the absence of the magnesium hydride.