Microfabricated Multiphase Reactors for the Selective Direct Fluorination of Aromatics

TLDR

The study introduces a silicon‑based microreactor that safely performs direct fluorination of toluene, overcoming the exothermic challenges of conventional large‑scale methods. The reactor uses cocurrent gas‑liquid contact at room temperature, enabling annular‑dry flow and allowing systematic investigation of conversion and product distribution across varying toluene concentration, fluorine ratio, solvent, and quenching conditions. A flow‑regime map (slug and annular‑dry) was established, showing that acetonitrile yields the highest ring‑fluorination selectivity, achieving up to 24 % combined ortho‑, meta‑, and para‑fluorotoluenes at 58 % toluene conversion.

Abstract

We describe a microchemical reactor built by silicon processing and metal deposition techniques that enables efficient and safe direct fluorination of toluene, a highly exothermic process difficult to implement conventionally on a macroscopic scale. Gas and liquid reagents were contacted cocurrently at room temperature in the microfabricated reactor, and gas−liquid distribution patterns were characterized. A flow regime map, containing slug and annular-dry flows, was obtained for liquid velocities relevant to gas−liquid reactions in microchemical systems. During annular-dry flow operation, the substrate conversion and product distribution were studied as a function of the operating conditions: toluene concentration, fluorine-to-toluene molar ratio, solvent type, and quenching conditions. Among the solvents tested, including acetonitrile, methanol, 1,1,2-trichloro-1,2,2-trifluoroethane, and octafluorotoluene, the highest selectivities toward ring fluorination were obtained in acetonitrile. At toluene conversions of 58%, a combined selectivity of ortho-, meta-, and para-fluorotoluenes of up to 24% was obtained.