Proposed Reaction Mechanism for the Kroll process based on Analysis of Experimental Results Obtained from a Bench-Scale Reactor

• The titanium sponge formation reaction in three distinct phases • Fluid flow plays a significant role in where the titanium sponge is formed • A novel description of the transport mechanism governing how titanium sponge is formed is presented The magnesiothermic reduction of titanium tetrachloride (TiCl 4 ) by molten magnesium (Mg) to form titanium (Ti) sponge under an argon (Ar) atmosphere at ∼1000 K is the dominant method to produce the precursor for aerospace-grade titanium. This process (known as the Kroll process) has received sparse attention in scientific literature despite its industrial ubiquity. The limited research activity has resulted in a lack of a comprehensive understanding of key reaction mechanisms, restricting possible avenues to process optimization and improvement. This study is a direct follow-up on previous work where a series of experiments were performed on a bench-scale Kroll reactor. A multi-phase, three-dimensional, thermal transient computational fluid dynamics model was developed and validated with experimental data, and was used to analyze the evaporation behaviour of TiCl 4 liquid and the resulting effect on the reactor fluid flow. The pressure and temperature data collected from the bench-scale Kroll reactor, along with the predicted evaporation rate, were used to estimate the evolution of the reaction rate of the Ti sponge formation process. A three-phase, isothermal, three-dimensional model of the settling behaviour of the reaction by-product magnesium chloride (MgCl 2 ) was also developed and showed to be qualitatively consistent with what was observed experimentally. The combination of the numerical models and detailed data analysis facilitated the proposal of a novel reaction mechanism describing the Kroll process.