Experimental Evaluation of a Membrane Micro Channel Reactor for Liquid Phase Direct Synthesis of Hydrogen Peroxide in Continuous Flow Using Nafion® Membranes for Safe Utilization of Undiluted Reactants

Abstract

In recent years, various modular micro channel reactors have been developed to overcome limitations in challenging chemical reactions. Direct synthesis of hydrogen peroxide from hydrogen and oxygen is a very interesting process in this regard. However, the complex triphasic process (gaseous reactants, reaction in liquid solvent, solid catalyst) still holds challenges regarding safety, selectivity and productivity. The membrane micro reactor system for continuous liquid phase H2O2 direct synthesis was designed to reduce safety issues by separate dosing of the gaseous reactants via a membrane into a liquid-flow channel filled with a catalyst. Productivity is increased by enhanced mass transport, attainable in micro channels and by multiple re-saturation of the liquid with the reactants over the length of the reaction channel. Lastly, selectivity is optimized by controlling the reactant distribution. The influence of crucial technical features of the design, such as micro channel geometry, were studied experimentally in relationship with varying reaction conditions such as residence time, pressure, reactant ratio and solvent flow rate. Successful continuous operation of the reactor at pressures up to 50 bars showed the feasibility of this system. During the experiments, control over the reactant ratio was found to be crucial in order to maximize product yield. Thereby, yields above 80% were achieved. The results obtained are the key elements for future development and optimization of this reactor system, which will hopefully lead to a breakthrough in decentralized H2O2 production.

Dynamic structural changes of supported Pd, PdSn, and PdIn nanoparticles during continuous flow high pressure direct H2O2 synthesis

“…To meet the safety regulations, most of the studies on the direct catalytic H 2 O 2 synthesis were performed with highly diluted gases in (semi-) batch reactors. 1,2 In addition, new and intrinsically safe concepts, that make use of membrane reactors 6,7 and electrochemical H 2 O 2 production, 3 have emerged. Recently, operando studies of the catalysts for H 2 O 2 production were reported by eliminating the explosion hazard by using thin capillaries as in situ reactors 8 or dissolving H 2 and O 2 at high pressures in separate liquid streams.…”

Simulation of Fluid Flow During Direct Synthesis of H2O2 in a Microstructured Membrane Reactor

“…Sketch of the microstructured membrane reactor for the direct synthesis of H 2 O 2 with gas resaturation, adapted with permission from Ref. 15 (a) and detailed scheme of the arrangement of a FGE in a microchannel covered by a PDMS membrane, adapted with permission from Ref. 34 (b).…”

“…In the simulation, the flow regime present in the liquid channel was assumed to be laminar, due to the low liquid flow rates in the range of milliliters per minute as used in the concept presented in 6 and 15 as well as channel geometries in the millimeter range. The maximum expected Reynolds number Re calculated in a void rectangular channel with a width of 6 mm and a height of 1.97 mm for an estimated, elevated flow rate of 16 mL min −1 was 75, which confirmed the validity of this assumption.…”

“…Their narrow channels hinder the propagation of an explosion and therefore massively increase the range of safe operation 14. The reactor concept presented in this paper combines both reactant separation with a membrane as well as microfluidic flow synergistically, targeting a new technology for on‐site synthesis of ready‐to‐use hydrogen peroxide solutions 6, 15.…”

Effect of Selectivity Enhancers on the Structure of Palladium during High-Pressure Continuous-Flow Direct Synthesis of Hydrogen Peroxide in Ethanol

“…The direct synthesis of H2O2 is an attractive route that involves reacting both molecular hydrogen and oxygen over a palladium-based supported catalyst in contact with a liquid phase in a single process stage 17 . The process so far has only entered the pilot phase 18 . The main reason impeding a viable process is the low selectivity 19 .…”