step a) forming a first product comprising unreacted methane, carbon, and hydrogen through methane pyrolysis by transferring a methane-containing feedstock to a first methane conversion step;

step b) separating a first gaseous mixture containing hydrogen and methane and solid carbonaceous materials from the first product, wherein a hydrogen (H₂)/methane (CH₄) molar ratio in the first gaseous mixture is adjusted within a range of 1 to 6;

step c) forming a second gaseous mixture containing hydrogen and acetylene through a methane coupling reaction by transferring the first gaseous mixture to a second methane conversion step,

wherein the second methane conversion step is performed through a direct non-oxidative methane coupling reaction by thermal conversion,

wherein in the second methane conversion step, a methane conversion is at least 35% and selectivity for acetylene is at least 60%, and

wherein a hydrogen (H₂)/acetylene (C₂H₂) molar ratio in the second gaseous mixture is adjusted within a range of 20 to 150;

step d) forming a third gaseous mixture containing hydrogen and ethylene by subjecting acetylene in the second gaseous mixture to selective hydrogenation in the presence of a hydrogenation catalyst; and

step e) separating and recovering hydrogen and ethylene, respectively, from the third gaseous mixture.