NOVELTY - The method comprises a synthesis step (10) that receives reactants including dihydrogen and carbon monoxide as input and produces a synthetic compound such as a fuel, water and top gases as output, recovering all or part of the top gases resulting from the synthesis step, and electrochemically producing dihydrogen by converting the top gases recovered in the recovery step. The producing step includes electrolyzing the recovered top gases in a side of an anode of an electrochemical apparatus. The method further comprises transferring the dihydrogen towards an entry of a synthesis reactor.    USE - The method is useful for performing chemical conversion of fuel such as coal, oil, biomass or natural gas, to form a synthesis compound such as liquid fuel including alkane and/or olefinic hydrocarbon (all claimed).    ADVANTAGE - The method is capable of improving the effectiveness of the chemical conversion in a cost-effective manner, improving recovery of the energy of the top gases, reducing or eliminating pollution, and reducing or eliminating the dilution of the carbon dioxide.    DETAILED DESCRIPTION - The method comprises a synthesis step (10) that receives reactants including dihydrogen and carbon monoxide as input and produces a synthetic compound such as a fuel, water and top gases as output, recovering all or part of the top gases resulting from the synthesis step, and electrochemically producing dihydrogen by converting the top gases recovered in the recovery step. The producing step includes electrolyzing the top gases recovered at the recovery step in a side of an anode of an electrochemical apparatus. The method further comprises: transferring the dihydrogen formed at the producing step towards an entry of a synthesis reactor implementing the synthesis step; cracking the top gases from of the synthesis step; collecting whole or part of the water output from of the synthesis step; collecting the carbon dioxide produced during the combustion reaction of the anode; heat exchanging between fluids consisting of the top gases recovered during the recovery step, the dihydrogen and/or water and/or carbon dioxide and/or dinitrogen from the electrolysis step, the gases from the cracking step, the water recovered during the collection step, and the carbon dioxide recovered during the collection step; gasifying (11) an input of combustible products and output reagents including part of dihydrogen and carbon monoxide used during the synthesis step in a gasification reactor; transferring the carbon dioxide from the carbon dioxide collection step towards an entry of the gasification reactor to form a carrier gas during the gasification step; recycling (16) the fraction of top gases from the synthesis step and not recovered at the recovery step; electrolyzing (15) water at high temperature using the fraction of water from the synthesis step and not recovered at the water collection step; transferring (28) the dihydrogen produced during the water electrolysis step towards an entry of the synthesis reactor; and/or transferring dioxygen produced during the water electrolysis step towards an entry of the gasification reactor to form a compound oxidizing during the gasification step. The step of electrolysis is assisted using the recovered water at the collection step. The step of assisted electrolysis is of anionic type and implements: a reduction reaction of water from a side of a cathode of the electrochemical apparatus to produce dihydrogen comprising a part of dihydrogen formed at the producing step and oxygen; and a combustion reaction on the anode side between the oxygen resulting from the reduction reaction and the top gases recovered from the recovery step to produce water and carbon dioxide. The step of cracking applied to the recovered gases at the recovery step is performed using a steam formed from the water recovered at the collection step and/or a re-used fraction of the total quantity of water from the electrolysis step. The electrolysis step is of protonic type and implements: an oxidation reaction on the side of the anode to produce carbon dioxide from the water and the gases recovered at the recovery step; and a reduction reaction on the side of the cathode of the electrochemical apparatus to produce dihydrogen comprising the part of the dihydrogen formed at the producing step. INDEPENDENT CLAIMS are included for:    (1) a chemical conversion installation for transforming fuel such as coal, oil, biomass or natural gas, into a synthesis compound such as liquid fuel including alkane and/or olefinic hydrocarbon; and    (2) a computer program.    DESCRIPTION OF DRAWING(S) - The figure shows a flow diagram of a chemical conversion method (Drawing includes non-English language text).    Synthesis step (10)    Gasification step (11)    Water electrolyzing step (15)    Top gases recycling step (16)    Dihydrogen transferring step. (28)