Improving diffusive mass transport in hierarchically structured Fischer-Tropsch catalysts

The pore system of a cobalt-based catalyst for Fischer-Tropsch synthesis is completely filled with liquid hydrocarbons at typical reaction conditions. This leads to lower catalyst utilization and, in particular, to reduced selectivity and reduced conversion with respect to long-chain hydrocarbons due to the formation of unwanted methane. The relationship between pore morphology and catalyst activity as well as product selectivity is investigated in this project in cooperation with the Institute for Chemical and Electrochemical Process Engineering (ICVT) and the Institute for Mechanical Process Engineering (MVT) of the Clausthal University of Technology. For this purpose, transport processes and chemical reactions in the liquid phase are numerically quantified within multimodal synthetically generated pore systems and real pore systems recorded by computer tomography at the ITM. The Lattice-Boltzmann and random walk particle tracking methods are used as numerical methods for the determination of the transport and reaction coefficients due to their high spatial resolution. The determined parameters are transferred to AG Turek of the ICVT for process simulation and catalyst characterization in a Fischer-Tropsch reactor model; together with AG Weber of the MVT, optimization strategies for layer structures of so-called building blocks are tested. Theoretical and experimental work in previous project phases has shown that larger, in particular parallel, cylindrical transport pores in the catalyst structure significantly improve the accessibility of the pore system. A further increase in catalyst utilization is to be achieved by coating the pore surfaces as omniphobically as possible, so that they remain largely free of liquid products. Such pores are produced in the project with different methods, theoretically modelled and experimentally tested.

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