Process for the thermal conversion of methane and a reactor for carrying out the process

A process for the thermal conversion of methane into hydrocarbons of higher molecular weight in a reaction zone having one elongated axis, comprising an upstream heating zone and a downstream cooling zone in which the effluents from the heating zone are cooled, said process comprising circulating a gaseous mixture containing methane in said heating zone in a direction of flow substantially parallel to the elongated axis of the reaction zone, wherein said heating zone comprises two walls of refractory material, at least one of said walls being disposed between outside walls of the reaction zone, said heating zone further comprising at least one longitudinal zone in which said gaseous mixture circulates, said longitudinal zone comprising a plurality of elements disposed in at least two layers within said refractory walls, which layers are substantially parallel to one another and substantially parallel to the elongated axis of the reaction zone, said elements forming in transverse projection a cluster of triangular, square or rectangular pitch, at least one of these layers comprising a series of sheaths containing electric heating means, thereby forming a layer of heating elements, said electric heating means thus being insulated from direct contact with the gaseous mixture containing the methane and said heating elements being grouped in successive transverse sections, each comprising at least one transverse row of elements, said sections being perpendicular to the elongated axis of the reaction zone, independent of one another and supplied with different amounts of electrical energy so as to define at least two parts in the heating zone;

• in the first part of the heating zone, heating the gaseous mixture to a temperature at least equal to approximately 1500.degree. C. and, in the second part of the heating zone, following the first part, maintaining the gaseous mixture at a temperature substantially equal to the maximum temperature to which it was raised in the first part, wherein said methane is converted into hydrocarbons of higher molecular weight;
• withdrawing an effluent from the second part of the heating zone;
• introducing said effluent into said downstream cooling zone;
• introducing a cooling fluid into the cooling zone to cool said effluent;
• and collecting said hydrocarbons of higher molecular weight at the end of the reaction zone.