(672g) Millisecond-Modulated Dynamic Gas Pulsing for Enhanced Surface Activity during Partial Oxidation of Methane to Syngas

The shift from centralized to distributed chemical manufacturing (DCheM) has driven innovation in microreactor technology and reactor operation. DCheM enables localized, small-footprint chemical processing in geographically-remote locations where transportation infrastructure is costly or inexistent. The adoption of competitive DCheM systems requires to operate reactors beyond the limits of thermodynamic equilibrium. Such operation windows are unlocked by short transport lengths in microreactors, enabling innovative modes of operation like dynamic catalysis that enhances reactor performance through the modulation of process inputs like temperature or pressure, in place of traditional static operation. Several studies have demonstrated rate enhancements from dynamic operation, which can be attributed to distinct phenomena: tuning of surface coverage for optimal energetics, operation in favorable thermodynamic conditions at the timescales of catalytic steps, or surface cleaning.

There’s a need for reactors with sharp input modulation at kinetic timescales and fast transport to study the contribution of each phenomenon to catalytic enhancement, without competing transport effects. To this end, we have designed a microreactor platform for oxidant/reductant feed switching to study the induced effects on reaction rate, selectivity, and catalyst deactivation for the partial oxidation of methane. The reactor is a wash-coated glass capillary designed to operate in plug flow for precise gas pulses and negligible thermal gradients. Pressure tests and residence time distributions validated near plug flow operation and millisecond residence times, critical for modulation above 1Hz. Feed modulation achieved square waveforms at frequencies up to 25Hz. The reactor is integrated in a gas chromatograph, providing fast MS/FID for analysis of products and temperature programmed oxidation to measure catalyst activity, selectivity, and coking. Dynamic experiments revealed that turnover responds to input concentration oscillations and time-averaged conversion at low temperature was maximized at the stoichiometric duty of complete oxidation which is dominant in an isothermal condition.