A reactor system for thermally treating a hydrocarbon-containing stream, that includes a pressure containment vessel comprising an interior chamber and a heat transfer medium that converts electrical current to heat and is positioned within the interior chamber of the pressure containment vessel, wherein the heat transfer medium comprises a first end face, a second end face, and channels extending between the first end face and the second end face. A process for thermally treating a hydrocarbon-containing stream includes introducing the hydrocarbon-containing stream into the reactor system, pressurizing the pressure containment vessel and the heat transfer medium without heating the pressure containment vessel or the heat transfer medium, supplying electrical current to the heat transfer medium, converting the electrical current to heat, heating the hydrocarbon-containing stream, and converting the hydrocarbon-containing stream to an effluent stream.