An apparatus and process for thermally de-manufacturing tires and other materials. The apparatus is a retort chamber with various zones in which tires are combusted to provide energy for the thermal depolymerization reaction, depolymerization takes place, and products leave the retort chamber. In one embodiment, the process reacts water with iron present in steel-belted tires to produce hydrogen, which helps to break sulfur-sulfur bonds in vulcanized materials. The water also helps control the temperature of the reaction, which allows for control over the types and relative amounts of the various depolymerization products.