TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Process: The metal atom of the metal cluster is bonded to at least one other metal of the metal cluster, preferably to six or fewer metal atoms of the metal cluster. Preferred Components: The hydrogenation catalyst (C1) is supported metal catalysts or supported metal sulfide catalysts, preferably supported transition metal catalysts or supported transition metal sulfide catalysts. The supported transition metal catalyst comprises one or more transition metals, preferably rhenium, rhodium, iridium, nickel, palladium or platinum. The supported transition metal sulfide comprises one or more transition metal sulfides, preferably sulfides of chromium, iron, rhenium, ruthenium, cobalt, rhodium, iridium, nickel, palladium, platinum or copper. The hydrogenation catalyst (C1) comprises a support of metal oxides, refractory oxides, metals, carbon or molecular sieves, preferably from silica, alumina, silica-alumina or carbon. The metal catalyst (C2) is alkane metathesis catalysts, preferably supported metal clusters, metal hydrides, organometallic compounds or organometallic hydrides, preferably grafted onto a solid support. The supported metal cluster comprises: one or more metals of groups 4, 5 and/or 6 of the periodic table of the elements, preferably tantalum; a solid support and a metal cluster, preferably bonding between the metals of the metal cluster, and bonding between the metal cluster and the solid support; and a solid support of a metal oxide, a refractory oxide, a molecular sieve, a zeolite or a metal phosphate. The catalyst from metal hydrides, organometallic compounds or organometallic hydrides, comprises at least metal comprising lanthanides, actinides or metals of groups 2-12, preferably transition metals of groups 3-12 of the periodic table of the elements, preferably niobium, tantalum, molybdenum, tungsten or rhenium. The catalyst is supported on, or grafted onto a solid support of metal or refractory oxides, sulfides, carbides, nitrides or salts, and carbon, mesoporous materials, organic/inorganic hybrid materials, metals or molecular sieves.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: In step (1), methane is used either alone or in the form of a mixture of methane, preferably in a major molar proportion, with one or more other alkanes preferably from the other alkanes present in natural gas, preferably the (C2+) alkanes having 2 carbon atoms and more, in the form of natural gas. The process further comprises a purification stage comprising removing from the methane or from the natural gas, one or more poisons capable of deactivating the hydrogenation catalyst (C1), the metal catalyst (C2) and/or one or more impurities, preferably nitrogen, prior to step (1); a preliminary stage comprising fractionating the components of the natural gas to separate and to isolate the methane from the rest of the natural gas comprising a mixture of the (C2+) alkanes having 2 carbon atoms and more prior to step (1). In step (1), the thermal cracking reaction is performed: by submitting methane to a temperature higher than 730 degrees C, preferably higher than 1200 degrees C; with a reaction time of 0.1-50 ms, preferably 0.1-10 ms; and by a high-temperature process from partial combustion processes, electrothermic processes or high-temperature pyrolysis processes. In step (1), the thermal cracking reaction is stopped by quenching the reaction mixture (M1) obtained at 50-300 degrees C; preferably 80-250 degrees C, preferably with a quench rate of 104-108, preferably 105-107 degrees C/seconds. The partial combustion process comprises preheating methane and oxygen preferably separately at 500-700 degrees C, passing the methane and oxygen thus preheated through a mixing zone and a burner into a cracking reaction zone where they are partially ignited, preferably at above 1000 degrees C, preferably above 1200 degrees C, with a reaction time of 0.1-50 ms to form the reaction mixture (M1) and quenching the reaction mixture (M1) when leaving the cracking reaction zone, preferably by water or a hydrocarbon liquid or an oil, preferably at 50-300 degrees C, with a quench rate of 104-108 degrees C/seconds. The electrothermic process comprises injecting methane into an arc furnace, preferably under an absolute pressure of 0.05-0.15 MPa, maintaining the methane in the arc furnace during a reaction time of 0.1-50 ms to form the reaction mixture (M1) and quenching the reaction mixture (M1) when leaving the arc furnace, preferably with the help of water or a hydrocarbon liquid or an oil, preferably at 50-300 degrees C, with a quench rate of 104-108 degrees C/seconds. The high-temperature pyrolysis process comprises cracking methane with a reaction time of 0.1-50 ms, in a refractory oven previously heated by combustion gases at 1000-3000 degrees C to form the reaction mixture (M1) and quenching the reaction mixture (M1) outside the refractory oven at 50-300 degrees C, with a quench rate of 104-108 degrees C/seconds. The reaction mixture (M1) comprising: acetylene, hydrogen, and optionally ethylene and unreacted methane or unreacted natural gas, preferably obtained in step (1) by a thermal cracking reaction carried out by an electrothermic process, is directly used in step (2) for converting acetylene and optionally ethylene into ethane; acetylene, hydrogen and optionally ethylene and unreacted methane or unreacted natural gas, is submitted, prior to step (2), to a fractionation comprising separating and preferably isolating the acetylene optionally in mixture with the ethylene and/or the unreacted methane or the unreacted natural gas, and optionally with the hydrogen, preferably in molar proportions with regard to acetylene identical to or lower than those in the reaction mixture (M1) or to a fractionation comprising separating from the reaction mixture (M1) at least a portion of the unreacted methane or the unreacted natural gas, preferably recycled to the thermal cracking reaction in step (1); and oxygen-containing products of carbon monoxide, carbon dioxide or unreacted oxygen, preferably obtained by a thermal cracking reaction carried out by a partial combustion process, is submitted, prior to step (2), to a fractionation comprising separating and eliminating the oxygen-containing products from the reaction mixture (M1). In step (2): the acetylene is used either alone or in the form of a mixture of acetylene, preferably in a major molar proportion, with ethylene and/or one or more alkanes, preferably with the ethylene and/or the unreacted methane or the unreacted natural gas present in the reaction mixture (M1), in molar proportions with regard to acetylene identical to or lower than those in the reaction mixture (M1); and the hydrogen is used either alone or in the form of a mixture of hydrogen with acetylene, preferably with the reaction mixture (M1). In step (2), the contacting is performed: at 0-400 degrees C, preferably 20-300 degrees C; under an absolute total pressure of 0.1-10 MPa, preferably 0.1-1 MPa; in the presence of one or more inert agents, preferably inert gases of nitrogen, helium or argon, and alkanes, preferably unreacted methane or the unreacted natural gas present in the reaction mixture (M1); and in a reaction zone of tubular or multi-tubular reactors, slurry reactors, fluidized bed reactors, mechanically agitated bed reactors, fluidized and mechanically agitated bed reactors, fixed bed reactors, moving bed reactors or circulating bed reactors. The reaction mixture (M2) comprising ethane and optionally unreacted acetylene, ethylene and hydrogen, and optionally one or more other alkanes, preferably methane or natural gas, is used directly in step (3) or is submitted, prior to step (3), to a fractionation comprising separating and preferably isolating the ethane or a mixture of the ethane with the methane or natural gas, and optionally with the hydrogen or to a fractionation comprising separating from the reaction mixture (M2), the unreacted acetylene, ethylene and optionally hydrogen, preferably recycled in step (2). In stage (3): the ethane is used either alone or in the form of a mixture of ethane, preferably in a major molar proportion, with one or more other higher alkanes, preferably the mixture of the (C2+) alkanes having 2 carbon atoms and more of the natural gas, in molar proportions with regards to ethane similar or identical to those existing in the natural gas; the ethane or the reaction mixture (M2) obtained in step (2) is used in mixture or in combination with a mixture of the (C2+) alkanes having 2 carbon atoms and more, obtained by fractionation of natural gas in a preliminary stage from which methane is derived and used in step (1); and the ethane or the reaction mixture (M2) obtained in step (2) and the mixture of the (C2+) alkanes are contacted either separately or simultaneously, preferably in the form of a pre-mixture, with the metal catalyst (C2). The step (3) is performed: at 20-400 degrees C, preferably 70-300 degrees C; under an absolute total pressure of 0.1-50 MPa, preferably 0.1-20 MPa; in the presence of at least one inert agent, preferably an inert gas, preferably nitrogen, helium or argon, and/or in the presence of hydrogen, preferably the hydrogen of the reaction mixture (M1), under a partial pressure of hydrogen of 0.1 kPa to 10 MPa, preferably 1 kPa to 1 MPa; in a reaction zone (Z1) which is either distinct and separate from a fractionation zone (F1) where stage (4) is performed, or arranged in a part of the fractionation zone (F1), preferably in at least one distillation column reactor; in a reaction zone comprising at least one reactor of static reactors, recycling reactors or dynamic reactors, or tubular or multi-tubular reactors, distillation column reactors, slurry reactors, fluidized bed reactors, mechanically agitated bed reactors, fluidized and mechanically agitated bed reactors, fixed bed reactors, moving bed reactors or circulating bed reactors; and by continuously introducing the ethane and optionally a mixture of the (C2+) alkanes pre-mixed or separated, into a reaction zone (Z1) containing the catalyst (C2) to form the reaction mixture (M3), and by continuously withdrawing at least a part of the reaction mixture (M3) out of the reaction zone (Z1) to subject the part of the reaction mixture (M3) to step (4) for separating the mixture of the (C3+), preferably (C5+) alkanes and isolating the mixture from the rest of the reaction mixture (M3) which is preferably returned into the reaction zone (Z1). The step (4) comprises one or more methods of fractionation of the reaction mixture (M3) comprising fractionation by change of physical state, preferably of gaseous/liquid phase of the mixture, preferably by distillation/condensation column or tower, fractionation by molecular filtration, preferably by semi-permeable and selective membrane, fractionation by adsorption, preferably by molecular sieve or any other adsorbent, fractionation by absorption, preferably by absorbing oil, fractionation by cryogenic expansion, preferably by expansion turbine, and fractionation by compression, preferably by gas compressor. The step (4) is performed by a double or multiple fractionation of the reaction mixture (M3) of an identical or different type, comprising separating and isolating the mixture of the (C3+), preferably (C5+) alkanes, in liquid form, the methane preferably recycled into step (1) for the methane conversion into acetylene, and optionally unreacted ethane and where applicable unreacted propane and/or butanes, preferably recycled into step (3) for the simultaneous ethane self- and cross-metathesis reactions. EXAMPLE - Methane was converted into acetylene by a thermal cracking reaction that was carried out by an electrothermic process. The methane was continuously introduced tangentially into the vortex chamber of the arc furnace and a reaction mixture (a) comprising acetylene, hydrogen, ethylene, soot and unreacted methane was produced continuously. The reaction mixture (a) was immediately withdrawn continuously out of the arc furnace and quenched by water with a quench rate of 106 degrees C/seconds to 200 degrees C. The reaction mixture (a) thus obtained comprised of acetylene, hydrogen and ethylene, and then contacted with hydrogen in the presence of hydrogenation catalyst to form a reaction mixture (b) comprising ethane and unreacted acetylene, ethylene and hydrogen, and some higher alkanes. A reaction mixture (c) comprising methane and a mixture of the (C3+) alkanes, preferably propane, butane, pentane and hexane, and unreacted ethane was formed by simultaneous ethane self- and cross-metathesis reactions. The reaction mixture (c) thus obtained was continuously submitted to a fractionation to separate and to isolate the mixture of the (C3+) alkanes in liquid form.