Manipulation of solid particle flow in microreactors for efficient chemical conversion

The incorporation of flowing nanoparticles or microparticles for use in (photo)catalysis as well as in the enhancement of mass transfer in microreactors opens a new avenue for chemical process intensification. In her thesis, Jie Zong studies nanofluids (dispersing nanoparticles into base fluids) as a pseudo-homogeneous phase in microreactors. The research reveals that adding nanoparticles could change the PTFE microreactor wall to be more hydrophilic due to nanoparticle deposition. This causes a lubricating liquid film around gas bubbles, which fundamentally alters the flow pattern. Besides, the measured pressure drop under N2-nanofluid slug flow can be accurately predicted by semi-empirical pressure drop models. Furthermore, the overall liquid-side volumetric mass transfer coefficient (kLa) could be significantly improved with increasing the gas-nanofluid flow ratio, nanofluid flow rate and nanoparticle concentration, or decreasing its size. 

Zong also investigated the reaction performance of heterogeneous (photo)catalytic reactions using (photo)catalyst suspensions both in batch and microreactors. She found a significant process intensification in microreactors for ofloxacin photodegradation mainly due to the shorter light penetration depth and improved gas-liquid mass transfer rate than those in batch. However, in the hydrogenation of levulinic acid to γ-valerolactone, the microreactor showed promise but faced challenges due to the poor catalyst dispersion, significant hydrogen permeation through the microreactor wall and limited γ-valerolactone yield. Finally, future directions for improving the long-term operational stability of nano-/micro-particle suspensions, the overall energy efficiency, and the development of closed-loop systems for continuous catalyst recovery and regeneration, still need to be further explored.