Exsolution of Solutes from Particles Formed by High-Temperature Gas-to-Particle Conversion Processes




Introduction: Gas-to-particle conversion is a route for producing both commodities, such as carbon black, fumed silica and pigmentary titania, and specialty particulate products extending down to the nanoscale size range. The particles produced by these aerosol processes may be multicomponent by design or by happenstance. The feeds may purposefully contain materials intended to dope or coat the product particles. But even if the feeds are ostensibly single component, they are rarely absolutely pure.

It is often of importance to understand and manipulate the fate of these secondary components. In this paper, we imagine a continuously operated plug flow contactor at steady state in which feeds rapidly react under adiabatic conditions at the entrance to produce a hot reaction mass comprised of gaseous byproducts in which a cloud of aerosol particles is suspended. The reaction mass flows in an axial direction through the contactor while heat is removed through the walls so that an axial temperature profile results. After sufficient cooling, gas-solid separations are employed to recover the particulate products for further processing while preparing the gaseous byproducts for either treatment or recycle.

We presume that the gas-to-particle conversion reactions produce particles comprised of a major component and a single secondary component. Further we presume that at reaction temperature, the secondary component is fully soluble in the particles. This paper develops a mathematical model by which one can calculate the extent of solute exsolution by solid-state diffusion under a thermodynamic driving force as the reaction mass flows axially while simultaneously being cooled.

Author: R. Bertrum Diemer

Keywords: Aerosol, Solid-State Diffusion, Heat Transfer, Multiscale Modeling


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8 pages


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