(223f) Design of Aerosol Coating Reactors by CFD

Core-shell particles facilitate incorporation of functional particles into
host (e.g. liquid or polymer) matrices like silica-coated TiO₂
pigments¹, carbon coated Cu for sensors² or superparamagnetic³ Fe₂O₃. Typically
core-shell particles are made in the liquid phase⁴ but there is keen interest to
develop gas-phase or aerosol coating processes that do not generate liquid
by-products, offer fewer process steps, easier particle collection and hermetic³ shells. Coating of particles in the
gas phase, however, is challenging, as particle motion and growth are much
faster than in liquids. As a result, it is difficult to control and develop a
scalable gas phase coating process. So, even commercially produced particles
made by aerosol routes (e.g. pigmentary TiO₂ made by the ?chloride?
process) are coated by wet processes⁴.

Here⁵, gas-phase (aerosol) coating is
elucidated in considerable detail, for the first time to our knowledge, by
computational fluid and particle dynamics for core particles (TiO₂)
and coating shells (SiO₂). Emphasis is placed on understanding the
influence of process variables (coating weight fraction and mixing intensity
(Figure 1) and geometry of core aerosol & shell precursor vapor) on
core-shell product characteristics by a trimodal aerosol particle dynamics
model⁶ accounting for SiO₂ monomer
generation, coagulation and sintering. The predicted extent of complete (or
hermetic) coating shells is compared to the measured photocatalytic oxidation
of isopropanol by such particles^7,8 and release of acetone. As hermetic SiO₂
shells prevent the photocatalytic activity of TiO₂, the performance
of coated particles is explained by the spatial distribution of shell thickness
on core particles with detailed reactor flow field analysis.

Financial support from the Swiss National Science Foundation (SNF) grant #
200021-119946/1 and European Research Council is gratefully acknowledged.

Figure 1 Influence of nitrogen
flow rate (mixing intensity) a) 5.8 l/min, b) 15.8 l/min and c) 30.8 l/min on
the coating precursor and coating shell thickness distribution inside the
aerosol coating reactor.

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