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Fischer-Tropsch-Synthesis : Modelling of Reaction-diffusion in a single Cobalt Catalyst Particle Using CO2-rich Synthesis Gas

Titelangaben

Pöhlmann, Ferdinand ; Jess, Andreas:
Fischer-Tropsch-Synthesis : Modelling of Reaction-diffusion in a single Cobalt Catalyst Particle Using CO2-rich Synthesis Gas.
In: German Society for Petroleum and Coal Science and Technology (Hrsg.): DGMK Tagungsbericht 2015-2. - Hamburg : Deutsche Wissenschaftliche Gesellschaft für Erdöl, Erdgas und Kohle e.V. , 2015 . - S. 187-193
ISBN 978-3-941721-56-2

Abstract

Carbon fixation in liquid hydrocarbons (e.g. gasoline, diesel oil, jet fuel, heating oil) is a promising solution on the major concern of carbon dioxide utilization. The formation of liquid hydrocarbons based on CO2 and renewable H2 (power-to-liquid) is a three-step process consisting of water electrolysis, reverse water-gas shift (RWGS), and Fischer-Tropsch synthesis (FTS). Here, the syngas for FTS always contains CO2 due to the incomplete carbon dioxide conversion step in the RWGS reactor (because of thermodynamic constraints). Hence, the question arises whether CO2 behaves as an active carbon source for Fischer-Tropsch products or acts only as diluting gas during the process. Moreover, under effective conditions (i.e. with particles of millimeter size as used in fixed bed reactors)
the FT reaction gets affected by internal mass transport limitations, which leads to an increasing H2-to-CO ratio inside the particle having an impact on local reaction rate and selectivity.
The characterization of the impact of transport pores on catalyst efficiency and productivity took place under intrinsic conditions as well as real diffusion affected conditions in a fixed bed reactor. The gradient of the synthesis gas ratio (H2/CO/CO2) inside a pellet was achieved by partial pressure variation at temperatures between 210 °C and 230 °C and total pressure of 3.0 MPa. With increasing surplus hydrogen, the methane selectivity rises if the CO concentration in the synthesis gas is lowered. At H2/CO-ratios > 10, CO2 also converts, but solely into methane. In order to characterize the effect of pore diffusion on catalyst efficiency, experiments with intact particles were conducted (H2/CO/CO2 = 2/1/1, T = 190-240 °C, ptotal = 3.0 MPa). As long as CO is present in the particle’s center, CO2 behaves like an inert species. However, with rising temperature the CO concentration gradient increases towards the center and regions free of CO arise inside the particle. Here, CO2 is mainly converted into mainly CH4 (selectivity of methane > 95 %C) resulting in a higher CH4-selectivity.
The mathematical model derived from our experimental results is in very good agreement with the data using kinetic parameters from intrinsic experiments and reveals CO-free regions where CO2 is converted and contributes to the product stream.

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Publikationsform: Aufsatz in einem Buch
Begutachteter Beitrag: Nein
Institutionen der Universität: Fakultäten > Fakultät für Ingenieurwissenschaften
Fakultäten > Fakultät für Ingenieurwissenschaften > Lehrstuhl Chemische Verfahrenstechnik
Fakultäten > Fakultät für Ingenieurwissenschaften > Lehrstuhl Chemische Verfahrenstechnik > Lehrstuhl Chemische Verfahrenstechnik - Univ.-Prof. Dr.-Ing. Andreas Jess
Fakultäten
Titel an der UBT entstanden: Ja
Themengebiete aus DDC: 500 Naturwissenschaften und Mathematik > 540 Chemie
600 Technik, Medizin, angewandte Wissenschaften > 600 Technik
600 Technik, Medizin, angewandte Wissenschaften > 620 Ingenieurwissenschaften
600 Technik, Medizin, angewandte Wissenschaften > 660 Chemische Verfahrenstechnik
Eingestellt am: 15 Okt 2015 07:28
Letzte Änderung: 15 Okt 2015 07:28
URI: https://eref.uni-bayreuth.de/id/eprint/20501