NFP

Structured microreactors

The fields of structured reactors in general and of microstructured reactors in particular are among the most active research areas in catalysis and reaction engineering.

Structured reactors present very important advantages, such as low pressure drop, high catalyst usage and reproducible flow patterns, however they typically suffer from a low catalyst loading, i.e., the amount of catalyst per unit volume is considerably lower than that attainable in a fixed bed reactor. The advantages (and disadvantages) of structured reactors are exacerbated in microreactors, where channel dimensions are reduced to attain high values of interphase area per unit reactor volume. Issues such as catalyst load, accessibility of the catalyst and adherence of catalyst layers, still present important challenges for a wider industrial use of microreactors.

In our laboratory we have devised ways of growing zeolite films directly on the inner surface of monolith and microreactor channels, avoiding the use of binders and improving the catalyst load and adherence. We are also investigating ways of combining zeolite film technology and processing methods borrowed from the microelectronics industry to obtain microreactors with unprecedented values of interphase area and high-flux micromembranes.

Reproducibly depositing the catalyst in the microchannels with a sufficient load is a difficult task. We investigate different synthesis methods (seeded and unseeded liquid phase hydrothermal synthesis, steam-assisted crystallization) to prepare zeolite films as catalytic coatings on microreactor channels, as well as the procedures to introduce a homogeneously distributed load of active component in the zeolite film.

Ultrahigh surface/volume microstructures

Regular structures of SiO2 microneedles and Si micromonoliths have been formed using processing methods similar to those used in the microelectronics field (with UPC). These structures have been used as supports for zeolite films, grown by seeded hydrothermal synthesis. The procedure leads to microstructured nanoporous coatings with external characteristic dimensions of a few microns in size and short diffusion lengths, allowing intimate fluid–solid contact. Depending on preparation conditions, the resulting films exhibit external surface to volume ratios in the 400,000–700,000 m2/m3 range. Some examples of zeolite-coated structures and a simulation of flow patterns (from L. Gandia) in a microneedle array are shown below.

Microreactors with unconventional (microwave) heating

We have recently started to investigate the possibility of attaining non-uniform heating patterns in microreactors by means of dielectric heating. To this end, catalytic films (zeolites) are grown on microreactor channels, and then elements capable of absorbing microwaves are introduced; we are interested in finding out the conditions to form temperature gradients between the catalyst surface and the bulk of the gas phase, and on the exploitation of these gradients to enhance reactor performance.

Main collaborations

- Prof. Volker Hessel, IMM Mainz
- Prof. Angel Rodriguez at the Polytechnic University of Catalonia, Barcelona, Spain.
- Profs Eduardo Miro y Alicia Ulla, University of Litoral, Argentina, Spain.

Some recent related publications

"Zeolite films and membranes. Emerging applications” Pina MP; Mallada R; Arruebo M; Urbiztondo M; Navascués N; de la Iglesia O; Santamaria J.. Micropor. Mesopor Mat. 144(2011) 19-27.
"Combustion of Volatile Organic Compounds at Trace Concentration Levels in Zeolite-Coated Microreactors”. Navascues, N; Escuin, M; Rodas, Y; Irusta, S; Mallada R; Santamaria J; Ind. Eng. Chem. Res. 49(2010) 6941-6947.
“Selective oxidation of CO in the presence of H₂, CO₂and H₂O, on different zeolite-supported Pt catalysts”, Sebastian V., et al., Appl. Catal., 366, 242-51, (2009).
“Preparation of zeolite films as catalytic coatings on microreactor channels”, V. Sebastián, et al., Microp. Mesop. Mater., 115, 147-55, (2008).
“Development of Etching Processes for the Micropatterning of Silicalite Films”, Pellejero, I., et al., Microp. Mesop. Mater., 114, 110-20, (2008).
“Preparation and characterization of Co-mordenite coatings onto cordierite monolith as structured catalyst”, Ulla, M.A.; et al., Catal. Today, 133, 42-48 (2008).
“Preparation of Pt/ZSM-5 films on stainless steel microreactors” De la Iglesia, O., et al., Catal. Today, 125, 2-10, (2007).
“Development of microstructured zeolite films as highly accessible catalytic coatings for microreactors”, Urbiztondo, M.A.; et al., J. Catal., 250, 190-194, (2007).

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