In-line Analysis of Chemical Reactions in Micro Reactors using Thermal Mass Flow Sensors

In this contribution we present a dual thermal mass flow sensor arrangement based on the thermo-transfer principle (calorimeter) for in-line monitoring of liquid phase chemical reactions in residence time micro reactors. Focus is on micro plants used in chemical micro process engineering. Studies are based on commercially available sensors for low mass flow rates using constant power mode. We chose the homogeneously catalyzed synthesis of butyl acetate as reactive model system for the characterization of the sensor system. Special attention was paid to the achievable sensitivity against relative changes in the isobaric heat capacity in the presence of two different flow pulsation regimes. Separation between flow and heat capacity induced changes in the sensor signal was investigated using pure organic solvents with known thermal properties. The chemical model system was processed in a residence time micro reactor integrated in a micro plant with one thermal mass flow sensor at the inlet and at the outlet of the micro reaction channel. Changes in the differential signal during chemical conversion and phase transition as a function of residence time were analyzed.