Mechanistic and constrained thermochemical modelling in chemical reactor engineering: Ti(IV) chloride oxidation revisited

In process and materials chemistry, computational modelling of complex reactive systems has been a long-time continuing process. The methodology based on numerical methods in mechanistic reaction kinetics as well as for fluid phase thermodynamics applying equations of state is well established. During the last two decades, however, thermodynamic multiphase technology based on the minimisation of Gibbs free energy has made progress in modelling both reactive flows and processing of functional materials. Recent advancements also include introduction of such new Gibbs'ian algorithms, which facilitate calculation of time-dependent changes in reactive multi-component multi-phase systems. Comparison between detailed kinetic mechanisms (DKMs) and multiphase thermochemical techniques has yet seldom been available. The present work describes a unique comparison between constrained Gibbs free energy calculation (with one constrained kinetic reaction rate) and detailed kinetic mechanism of 67 reversible reactions between 28 species, as performed for the industrially interesting Titanium(IV) chloride oxidation process. When confined to gas phase kinetics, the calculated results show fair agreement between the two different techniques. However, comparison with observations from an experimental plug flow reactor suggests that the formation of a solid Ti-oxide phase in the models becomes a necessity. The applicability of the alternative simulation techniques in chemical reactor engineering is shortly discussed.