(34c) Kinetics of High-Pressure Multiphase Homogeneous Catalyst Systems in Continuous Flow Microreactors

Microreactors enable the study of multiphase catalyst systems at high-pressures that were previously difficult to attain on the laboratory scale. By studying catalyst systems at industrially relevant conditions, it may be possible to reduce the time and cost of developing new catalyst systems. Reaction kinetics are then used to optimize commercial processes. The reduced length scales, characteristic of microchemical systems, provide additional benefits such as enhanced heat and mass transfer, a reduction of hazard waste, and access to high pressures. The improved heat and mass transfer allow for kinetics to be probed at isothermal conditions and in the absence of complicating mass transfer effects.

A high-pressure microreactor system was built to harness these benefits. The system allows for the multiphase study of homogenously catalyzed systems. The multicomponent gas phase is delivered simultaneously with a liquid stream resulting in regular segmented (slug) flow. The isobaric system is operated at pressures of up to 100 bar. Gas and liquid flow rates, and therefore residence time, are specified independently of temperature. The system is capable of being operated at temperatures of at least 300°C and residence times of up to 15 minutes. Both online analysis, using a new Mettler-Toledo attenuated total reflection FTIR flow cell, and sample collection for offline analysis can be performed simultaneously.

The hydroformylation of terminal alkenes, catalyzed by HRh(CO)(PPh₃)₃, was studied in the new high-pressure microfluidic system. The literature contains few data on the kinetics of hydroformylation, much of which are contradictory. Apparent activation energies have been determined at a number of conditions. A design of experiment was completed to enable a systematic determination of the kinetic parameters. These experiments demonstrate the capabilities of the high-pressure microreactor system. Applications to other gas-liquid systems are also discussed.