Miniaturized and
microstructured reactors in process engineering
are essential for a more decentralized, flexible, sustainable, and
resilient chemical production. Modern, additive manufacturing methods
for metals enable complex reactor-geometries, increased functionality,
and faster design iterations, a clear advantage over classical subtractive
machining and polymer-based approaches. Integrated microsensors allow
online, in situ process monitoring to optimize processes like the
direct synthesis of hydrogen peroxide. We developed a modular tube-in-tube
membrane reactor fabricated from stainless steel via 3D printing by
laser powder bed fusion of metals (PBF-LB/M). The reactor concept
enables the spatially separated dosage and resaturation of two gaseous
reactants across a membrane into a liquid process medium. Uniquely,
we integrated platinum-based electrochemical sensors for the online
detection of analytes to reveal the dynamics inside the reactor. An
advanced chronoamperometric protocol combined the simultaneous concentration
measurement of hydrogen peroxide and oxygen with monitoring of the
sensor performance and self-calibration in long-term use. We demonstrated
the highly linear and sensitive monitoring of hydrogen peroxide and
dissolved oxygen entering the liquid phase through the membrane. Our
measurements delivered important real-time insights into the dynamics
of the concentrations in the reactor, highlighting the power of electrochemical
sensors applied in process engineering. We demonstrated the stable
continuous measurement over 1 week and estimated the sensor lifetime
for months in the acidic process medium. Our approach combines electrochemical
sensors for process monitoring with advanced, additively manufactured
stainless steel membrane microreactors, supporting the power of sensor-equipped
microreactors as contributors to the paradigm change in process engineering
and toward a greener chemistry.