Development of a bench-scale Kroll reactor: Experimental results and preliminary findings

The Kroll process remains the predominant method for large-scale titanium sponge production, involving the reduction of titanium tetrachloride (TiCl₄) with molten magnesium (Mg) under an argon (Ar) atmosphere at 1000-1100 K producing molten magnesium chloride (MgCl 2 ) as a by-product. Despite its widespread industrial use, the Kroll process has received limited attention in the scientific literature, with existing studies presenting limited process data with differing interpretations. This lack of comprehensive understanding has left key reaction mechanisms in the commercial process poorly defined. This study presents four experiments with varying process conditions using a benchtop-scale reactor with high-resolution temperature and pressure instrumentation. These process conditions include, with and without the initial presence of MgCl 2 , varying feed rates and different materials present in the reactor to assess their ability to serve as substrates for Ti-sponge formation. The experimental results showed that the Ti sponge can grow on any substrate material irrespective of electrical conductivity, indicating that electron transport through crucible walls is not essential for Ti growth. Instead, it was found that the capillary action of Mg through porous Ti sponge was the driving force behind the continuation of the reaction. Furthermore, the reaction rate changed throughout the TiCl 4 feed, suggesting a changing surface area where the heterogenous reaction can occur.