With his master’s thesis on the Fischer-Tropsch synthesis (FTS), the production engineering student Alexander Zimmermann from the University of Bremen was so convincing that he has now been awarded the Bremen Engineering Prize 2022 by the Bremen district association of the Association of German Engineers (VDI). . “The winner of this year’s engineering prize has worked to improve this process as part of his master’s thesis with impressive results,” says the reason for the renowned award. “The current energy crisis and lack of raw materials makes the Fischer-Tropsch synthesis more interesting than ever.”
The Fischer-Tropsch synthesis was discovered in Germany and developed to technical maturity in a short time from 1920. The process is experiencing a renaissance in the 21st century because liquid fuels will also have to be produced from alternative raw materials such as natural gas, coal or biomass in the future.
Up to now, tube bundle reactors and bubble column reactors have prevailed for the technical implementation of the highly exothermic reaction. Since both reactor technologies have disadvantages, new reactor concepts are being investigated. Although fixed-bed reactors with a bed of highly porous pellets have the potential for a significant process intensification of the FTS, a mass transport limitation usually prevents this from actually being exploited. During the reaction, the reaction products also accumulate in the pores, so that the material flow is greatly slowed down.
Provided new bases for the procedure
In his master’s thesis “Mass transport of product mixtures of FTS analysis using NMR”, Alexander Zimmermann provided important new basics for this method.
The aim of this work was to understand the connection between the pore structure and mass transfer behavior of the reaction products and thus to enable the selection of the optimal structure of the pellets used for the highest possible throughput reactor operation. Alexander Zimmermann examined special pellets that support rapid mass transport and an improved reaction process thanks to hierarchically branched pore structures.
To this end, as part of his master’s thesis, he undertook numerous experiments using Nuclear Magnetic Resonance (NMR) – similar to the imaging MRI used in medicine – to evaluate the mass transport in the pellets used for catalysis. The specialty was to characterize the behavior of a mixture of the reaction products in the pores of the pellets used. It was shown that the special hierarchical pore structure has a particularly advantageous effect on the mass transport of such mixtures.
Efficiency can be increased significantly
From this new perspective, it was possible to show new potential advantages of this pore structure for the mass transport of the FTS. The economic efficiency of this process can thus be increased considerably. The industrial application of these new findings can significantly improve the intensity and quantity of the basic chemical substances obtained in this way. “Alexander Zimmermann’s work makes it clear that we can still use considerable development potential on the way to improving the climate,” concludes the VDI.
The work was supervised by Professor Jorg Thöming (Faculty of Production Engineering), who also recommended his students for the prize. “What impressed me about Alexander Zimmermann’s master’s thesis was how deeply he penetrated the demanding physical theory required to solve the very challenging task in a short time. So well penetrated that he was able to develop a sophisticated test plan for measurements using pulse gradients. These types of measurements were new to us in the field.”
His clear and well thought-out analysis of the measurement data shows how well Zimmermann understood the theory, which was new to him. “He was then able to use his results in an exemplary manner to solve the process engineering task. It consisted of finding out how the pores in catalysts have to be structured in order to also allow two-phase mass transport in the best possible way. His results bring the goal of cheaper synthetic fuels within reach,” says Jorg Thöming.
