Reactive particle precipitation in liquid microchannel flow

Continuous precipitation by mixing of two fluids is a simple and important method to produce nanoparticles for many industrial applications in specialty chemistry, pharmacy, or food industry. The convective mixing and mass transfer determine the nucleation and growth of the nanoparticles, resulting in the final particle size distribution. We have studied the ability of T-shaped silicon micromixers for reactive precipitation of nanoparticles. The mixer chips have a straight mixing channel to minimize particle attachment and blocking. The experimental results show a narrow particle size distribution for the precipitation of barium sulfate (BaSO4) over a wide operation range. The particle nucleation is modelled with the classical thermodynamic nucleation theory. The growth of a single particle is analytically described by the diffusive mass transfer in its vicinity and the Sherwood number, while particle interactions are neglected. The T-shaped micromixers are also used to investigate azo coupling under industrial conditions. With these results, basic rules for design and operation of the mixing device are given to prevent clogging and reduce fouling.