Direct synthesis of hydrogen peroxide in a microreactor

The direct synthesis of hydrogen peroxide in a microreactor is a safe and efficient process. Conventionally, hydrogen peroxide is produced using the anthraquinone autooxidation process, which is rather complex and can only be performed cost-effectively on a large scale. As a result, hydrogen peroxide needs to be stored and transported to locations where is it used with all the risks involved. The direct synthesis of hydrogen peroxide in a single step over a palladium catalyst, on the other hand, allows for the production of ultra-pure hydrogen peroxide on a smaller scale, which can then be used directly without the need to add stabilizers, which can affect the processes in which it is used. The hydrogen peroxide direct synthesis, however, has two main issues. Firstly, the simultaneous use of hydrogen and oxygen in a conventional reactor can be dangerous due to explosion risks. Secondly, the catalysts used in the hydrogen peroxide direct synthesis also catalyze the decomposition of hydrogen peroxide once higher concentrations are produced. In this presentation we will show the development of an efficient wall-coated catalytic microreactor system for the direct synthesis of hydrogen peroxide over a bimetallic gold-palladium catalyst. In this microreactor we can work safely with non-diluted mixtures of hydrogen and oxygen (50vol% each). At these reaction conditions, we can achieve hydrogen peroxide productivities which are an order of magnitude higher than at the dilute (4 vol% H2 and O2) conditions which are conventionally used. In addition to this leap in productivity, also the reaction selectivity improves dramatically from 30 to 70 %. This increase in selectivity we will explain using a kinetic study, which shows that a higher surface occupancy on the catalyst surface of the reactants at these higher partial pressures prevents the peroxide decomposition. In an optimization study, we will show that using this technology, it is possible to produce 1 wt% H2O2 at a high selectivity (>80 %) in a single step. It is possible to produce up to 5 wt% of hydrogen peroxide in a single step, however, in that case the peroxide decomposition rate becomes high and the overall selectivity drops to only about 25%. In the final part of the presentation, we will present our current research in which we attempt to combine a high productivity with a high selectivity by taking the process intensification one step further: directly combining the hydrogen peroxide production with its consumption in a fine chemical selective oxidation. The direct usage of the peroxide in the same microreactor keeps its concentration low, thereby preventing its decomposition.