| dc.description.abstract | Selecting a reactor technology for the Fischer-Tropsch Synthesis (FTS) is a trade-off since each reactor type (reaction phase) has its strengths and weaknesses. In order to overcome many of the limitations of the conventional FTS reactors, supercritical fluids (SCF) were proposed to be used as a reaction medium. SCF act as a unique reaction media, offering single-phase operation with diffusivities similar to those of gases and solubilities and heat transfer properties similar to those of liquids.
Even though SCF were applied in a number of studies showing promising enhancements since the late 1980s, none of these studies were able to move the supercritical Fischer-Tropsch (SC-FTS) technology beyond the lab-scale. The aim of this project was to overcome this by commissioning a bench-scale, high-pressure reactor unit that can provide better understanding of the FTS reaction, optimize the reaction behavior for typical large-scale FTS processes, and investigate/validate the potentials of enhancements of the FTS under supercritical phase.
This thesis describes the methods followed in commissioning and operating this unique reactor unit. In addition, to accomplish the project goals, a sophisticated experimental campaign was developed, starting with the catalyst (15 wt% Co/Al2O3) preparation and finishing with the product analysis using multiple gas chromatographs (GCs). The validation study showed that under SC-FTS operation, CO conversion increased by 14 %, methane selectivity decreased from 15 to 2.2 normalized wt%, middle distillates and wax selectivities increased by 35 wt% and 75 wt%, respectively, and the chain growth probability increased from 0.76 to 0.85, while total olefin formation rate increased by 62 %. The aforementioned improvements were attributed to the in-situ wax extraction ability of SC solvents, their ability to extract olefins before they undergo secondary reactions, and their liquid-like heat capacity allowing for better reaction heat removal. The obtained results demonstrate that the SC-FTS technology has the potential to substitute conventional FTS processes. Nevertheless, deeper understanding of the reaction mechanism and the reaction mixture thermo-physical properties under SC phase as well as techno-economic evaluation of this technology are required before it can be commercialized. | en |
