Process for chemically treating scrap tyres, comprising: a) grinding the tyres and removing the inorganic material; b) melting the material from step a); c) devulcanizing the molten material from step b) according to the reaction R1 R1: [-CH 2 -]n-S-[-CH 2 -]m + H 2 = [-CH 2 -]n* + [-CH 2 -]m* + H 2 S where m and n indicate non-identical lengths of the macromolecules in terms of carbon atoms and the asterisk indicates the possible presence of at least one olefin unsaturation, at a temperature comprised between 300 and 400°C, at a pressure comprised between 10 and 150 bar, said reaction R1 being possibly associated with the saturation reaction R2 of said possible at least one olefin unsaturation: R2: [-CH 2 -]n* + [-CH 2 -]m* + H 2 = [-CH 2 -]n + [-CH 2 -]m d) converting the plastics from step c) into products of commercial value, wherein step c) is carried out in the presence of catalysts based on cobalt oxide or molybdenum oxide possibly supported on alumina in a homogeneous or heterogeneous fixed or mobile (fluidized or dragged) bed reactor this process comprises a step c-1) wherein a thermal, catalytic or electrochemical splittingis carried out of hydrogen sulphide formed in the reaction R1 of step c) to hydrogen and sulphur according to the reaction R3: R3: H 2 S = H 2 + 1/x Sx and the formed hydrogen is recycled r to step c); the commercial products obtained in step d) are selected from: - linear or branched light and higher boiling saturated or unsaturated: hydrocarbons, paraffinic or naphthenic/ aromatic hydrocarbons; - syngas having different S ratios (H2 over CO and CO2) in co-presence of light hydrocarbons and olefins; - highly added values chemicals selected from methanol, dimethyl ether and acetic acid-. a) grinding the tyres and removing the inorganic material; b) melting the material from step a); c) devulcanizing the molten material from step b) according to the reaction R1 R1: [-CH 2 -]n-S-[-CH 2 -]m + H 2 = [-CH 2 -]n* + [-CH 2 -]m* + H 2 S where m and n indicate non-identical lengths of the macromolecules in terms of carbon atoms and the asterisk indicates the possible presence of at least one olefin unsaturation, at a temperature comprised between 300 and 400°C, at a pressure comprised between 10 and 150 bar, said reaction R1 being possibly associated with the saturation reaction R2 of said possible at least one olefin unsaturation: R2: [-CH 2 -]n* + [-CH 2 -]m* + H 2 = [-CH 2 -]n + [-CH 2 -]m d) converting the plastics from step c) into products of commercial value, step c) is carried out in the presence of catalysts based on cobalt oxide or molybdenum oxide possibly supported on alumina in a homogeneous or heterogeneous fixed or mobile (fluidized or dragged) bed reactor this process comprises a step c-1) wherein a thermal, catalytic or electrochemical splittingis carried out of hydrogen sulphide formed in the reaction R1 of step c) to hydrogen and sulphur according to the reaction R3: R3: H 2 S = H 2 + 1/x Sx and the formed hydrogen is recycled r to step c); the commercial products obtained in step d) are selected from: - linear or branched light and higher boiling saturated or unsaturated: hydrocarbons, paraffinic or naphthenic/ aromatic hydrocarbons; - syngas having different S ratios (H2 over CO and CO2) in co-presence of light hydrocarbons and olefins; - highly added values chemicals selected from methanol, dimethyl ether and acetic acid-. - linear or branched light and higher boiling saturated or unsaturated: hydrocarbons, paraffinic or naphthenic/ aromatic hydrocarbons; - syngas having different S ratios (H2 over CO and CO2) in co-presence of light hydrocarbons and olefins; - highly added values chemicals selected from methanol, dimethyl ether and acetic acid-.