Greener approaches to organic synthesis using microreactor technology.

The methods used to deposit a catalyst on structured surfaces are reviewed. Physical methods such as PVD and chemical methods (sol–gel, CVD, direct synthesis, etc.) are described. The coating of catalysts based on oxide, zeolite or carbon support is detailed on various surfaces such as silicon or steel microstructured reactors, cordierite monoliths or foams, fibres, tubes, etc.

Review on methods to deposit catalysts on structured surfaces

In the frame of globalization and sustainability, process intensification, a path to the future of chemical and process engineering (molecules into money)

https://pure.rug.nl/ws/files/56661244/Multiphase_flow_processing_in_microreactors_combined.pdf

Multiphase flow processing in microreactors combined with heterogeneous catalysis for efficient and sustainable chemical synthesis

Microreactor numbering-up in multi-scale networks for industrial-scale applications: Impact of flow maldistribution on the reactor performances

Mass transfer limitations in microchannel reactors

The selective oxidation of isoprene to citraconic anhydride over vanadia-supported catalysts is used as a test reaction for the comparison of different reactors. A metal microchannel reactor reveals a behaviour that indicates a better isothermicity than a laboratory-scale tubular reactor. However, the blank activity of the stainless steel microchannels with their high surface-to-volume ratio seems to decrease the catalytic performance. A ceramic microchannel reactor has an intermediate isothermicity and less blank activity. From the experiments, additional features like pressure drop or mass transfer can be evaluated. The generic differences between microchannel reactors and conventional laboratory-scale reactors are discussed in the framework of recent literature. It becomes obvious that microchannel reactors may currently still suffer from problems like high blank activity or intricate catalyst application, but do have intrinsic advantages like the high isothermicity. On a general note, the different scaling of length, surface area and volume makes a straightforward comparison between microchannel reactors and conventional reactors far from trivial.

Comparison of Microchannel and Fixed Bed Reactors for Selective Oxidation Reactions: Isoprene to Citraconic Anhydride

Selective oxidation of isoprene to citraconic anhydride

In recent years, particulate filters have become mandatory in almost all gasoline-powered vehicles to comply with emission standards regarding particulate number. In contrast to diesel applications, monitoring gasoline particulate filters (GPFs) by differential pressure sensors is challenging due to lower soot masses to be deposited in the GPFs. A different approach to determine the soot loading of GPFs is a radio frequency-based sensor (RF sensor). To facilitate sensor development, in previous work, a simulation model was created to determine the RF signal at arbitrary engine operating points. To ensure accuracy, the exact dielectric properties of the soot need to be known. This work has shown how small samples of soot-loaded filter are sufficient to determine the dielectric properties of soot itself using the microwave cavity perturbation method. For this purpose, mixing rules were determined through simulation and measurement, allowing the air and substrate fraction of the sample to be considered. Due to the different geometry of filter substrates compared to crushed soot samples, a different mixing rule had to be derived to calculate the effective filter properties required for the simulation model. The accuracy of the determined mixing rules and the underlying simulation model could be verified by comparative measurements on an engine test bench.

/pdf/mixing-rules-for-an-exact-determination-of-the-dielectric-2qyxg6ws.pdf

Mixing Rules for an Exact Determination of the Dielectric Properties of Engine Soot Using the Microwave Cavity Perturbation Method and Its Application in Gasoline Particulate Filters

Abstract Hydrogen combustion engines can contribute to CO 2 -free mobility. However, they produce NO x emissions, albeit only to an extremely small extent when operated very leanly. One approach to reduce these emissions even further is to use exhaust gas aftertreatment systems like NO x storage catalysts (NSC). So far, they have mainly been used in diesel or gasoline applications. This contribution shows that under conditions such as those prevailing in hydrogen engines, the NSC can achieve not only a higher storage capacity for nitrogen oxides (NO x ) but also a higher conversion. To ensure permanently high conversion rates, the amount of stored NO x has to be monitored permanently to prevent NO x breakthroughs. Conventional NO x sensors may not be accurate enough due to the very low NO x emissions. The functionality of the radio frequency (RF) sensor, which enables a direct determination of the NO x loading, is demonstrated for operation under hydrogen conditions. Furthermore, the influence of rich exhaust gas on the RF signal, which is relevant for a correct NO x loading determination during regeneration, is analyzed. 

/pdf/on-the-suitability-of-nox-storage-catalysts-for-hydrogen-ho0g9swt.pdf

St. Walter

Papers

Mass transfer limitations in microchannel reactors

Comparison of Microchannel and Fixed Bed Reactors for Selective Oxidation Reactions: Isoprene to Citraconic Anhydride

Selective oxidation of isoprene to citraconic anhydride

Mixing Rules for an Exact Determination of the Dielectric Properties of Engine Soot Using the Microwave Cavity Perturbation Method and Its Application in Gasoline Particulate Filters

On the Suitability of NOx-Storage-Catalysts for Hydrogen Internal Combustion Engines and a Radio Frequency-Based NOx Loading Monitoring