The standard Falling Film Microreactor (FFMR-STANDARD) developed by IMM in which liquid films of a few tens of micrometer thickness and interfacial areas up to 20,000 m2/m3 combined with an effective heat exchange can be obtained represents a broadly used microstructured lab tool in the area of gas/liquid contacting (see e.g. [1-3]). In the context of the German public funded project µ.Pro.Chem (Förderkennzeichen 16SV1991) with the partners BASF AG, Evonik Degussa GmbH and IMM one topic is to transfer this lab-scale device which is successfully applied for the Evonik Degussa GmbH process of an ozonolysis towards pilot scale and production scale. Targeted pilot throughput is thereby for the liquid about of 10 l/h which represents a one-hundred fold increase compared to the lab-scale device FFMR-STANDARD. To reach production scale a further increase of throughput by a factor of 10 – 100 is required.
The followed approach by IMM to reach pilot scale is first to design a larger base unit with an about tenfold increase of structured surface and then in a next step to design a pilot reactor based on (tenfold) internal numbering-up. Therefore in a first step a falling film microreactor with a larger reactor plate has been developed and realized. The microchannel width and depth has been kept constant compared to FFMR-STANDARD while both the number of channels and the length of the channels have been increased by a factor of 100.5. The principal design in this new falling film microreactor (FFMR-LARGE) – removable reaction plate in a housing bearing the feeding lines – is similar to the one of the FFMR-STANDARD. Some modifications have been incorporated to improve or ensure equal distribution of gas and liquid in the reactor. The next step then was to come to a pure plate design for this larger base unit as basis for the later internal numbering-up. While the reaction plate structure for the gas/liquid contacting was kept, major changes have been necessary to realize the functionality of the housing with regard to stability and feed distribution by only structuring plane reactor plates by wet-chemical etching. Furthermore, the reactor plates design has been adjusted to the selected sealing process by brazing. Corresponding prototypes (called STACK-1x-FFMR-LARGE) have been successfully realized including a version with an open gas chamber which allows visual observation of the reaction plate. Finally, a pilot-scale reactor consisting of a stack of ten of these plate-based functional units has been realized (called STACK-10x-FFMR-LARGE).
The reactor development work has been accompanied and supplemented by experimental works dealing with the characterization of the reactor performance and also with studying equal distribution of gas and liquid in the reactor for all developed reactor types. The ozonolysis reaction has been performed by Evonik Degussa GmbH itself and can not be reported here. The reactor performance has additionally been studied by IMM using the CO2 absorption in an aqueous sodium hydroxide solution and by an oxidation reaction of an organic compound by pure oxygen. These investigations have confirmed that the performance of the larger base unit FFMR-LARGE can be operated at a tenfold throughput compared to FFMR-STANDARD while keeping similar reactor performance (see also [4]). Via the CO2 experimentation it was shown also that the step from FFMR-LARGE to STACK-1x-FFMR-LARGE has not changed reactor performance and thereby confirmed the design. Furthermore, just recently the experimentation with the pilot-scale reactor STACK-10x-FFMR-LARGE has started. So far already a reactor performance of about 70% at an again tenfold increased throughput has been reached. The works here are continuing to confirm 100% performance. Gas and liquid equal distribution in different falling film microreactors has been studied by different methods: evolution of the liquid film via dosing of a dyed liquid, liquid flow rate measurements per channel and discoloring of a with phenolphthalein dyed sodium hydroxide solution during CO2 absorption. Thereby, the evaluation of the different reactor designs has been possible.
Concluding an outlook on the approach to reach production scale by a combination of internal and external numbering-up will be given.
[1] Ehrich, K., Linke, D., Morgenschweis, K., Baerns, M., Jähnisch, K., Chimia 56 (2002) 647-653.
[2] Yeong, K.K., Gavriilidis, A., Zapf, R., Kost, H.-J., Hessel, V., Boyde, A., Exerpimental Thermal and Fluid Science, 30 (2006) 463-472.
[3] Löb, P., Löwe, H., Hessel, V., Journal of Fluorine Chemistry 125 (2004) 1677-1694.
[4] Vankayala, B.K., Loeb, P., Hessel, V., Menges, G., Hofmann, C., Metzke, D., Krtschil, U., Kost, H.-J., International Journal of Chemical Reactor Engineering, accepted for publication.