(255g) Converting a Gas Chromatograph to Microflow Reactor Capable of Vapor-Phase Kinetic Measurements

Authors: 
Kumar, G. - Presenter, Dupont CRD/EXP ST
Chatzidmitriou, A., University of Minnesota
Abdelrahman, O., University of Massachusetts Amherst
Dauenhauer, P., University of Minnesota
We report the instrumentation of a fully automated vapor-phase microflow reactor as integrated within a gas chromatograph (GC) unit capable of measuring the reaction kinetics of vapor-phase catalytic chemistries with volatile feeds at near ambient pressures and mild temperature conditions (403-543 K). A splitless liner is used to load the catalyst bed, while two six-port gas sampling valves are used to operate the reactor in three possible configurations: a) Material pre-treatment, where the catalysts can be calcined to up to 400°C in air; b) Reactor bypass mode, and c) Reactant introduction and product quantification mode, where the feed contacts the catalyst bed followed by periodic gas sampling injections of reactor effluent to the back inlet, enabling a transfer of kinetic information from the reactive front inlet portion of the GC, to the analytical chromatography back inlet portion. Differences between the reactor set temperature (indicated by GC) and catalyst bed temperature are found to be negligible in the axial region in the range 0.15 < h/H < 0.35 inside the reactor tube (I.D.= 4 mm), while they are significantly higher (>10%) outside this region, highlighting that the axial location of the catalyst bed is sensitively linked to the temperature control attainable on the setup. Residence time distribution studies with ethanol pulses establish Peclet numbers >100 (nearly plug flow hydrodynamics) at moderate diluent gas flowrates (> 40 sccm He). A combination of four Brønsted acid catalyzed reactions, namely the dehydration of ethanol, 2-propanol, 1-butanol, and 2-methyltetrahydrofuran (2-MTHF) on a solid acid HZSM-5 (Si/Al 140), is carried out for the measurement of apparent reaction kinetics. The resultant product distributions, proton-normalized reaction rates, and activation barriers agree well with previous measurements performed in conventional packed bed reactors, validating the setup’s broad applicability under low conversion (<15%) and mild temperature (403-543 K) conditions.