CaC2 production with pulverized feeds was proven viable at temperatures about 400 degrees C lower than that required by the current electric arc technology (2100-2200 degrees C), which led to development of an autothermal process. For the purpose of reactor design, the reaction mechanism of coke (C) with CaO at temperatures up to 1750 degrees C is studied in a thermogravimetric analyzer (TGA) coupled with a mass spectrometer (MS). Results indicate that the reaction of C with CaO generally proceeds in three stages, starting at 1460 degrees C for CaC2 formation, followed by reaction of CaC2 with CaO and by decomposition of CaC2. The second stage is observable only at the complete consumption of C while the third is controlled by surface evaporation of Ca. Reaction behavior at the surface of coke and CaO particles is proposed, including the three-stage reactions and the role of CaC2-CaO eutectics, that promotes CaO diffusion and CaC2 production.