Development and scale-up design of a microchannel Fischer-Tropsch synthesis reactor for synthetic fuel production from biomass synthesis gas
Thesis DisciplineChemical Engineering
Degree GrantorUniversity of Canterbury
Degree NameMaster of Engineering
Today’s society has become reliant of fossil energy based transportation fuels which are unsustainable and produce significant amounts of pollutants. With diminishing fossil energy reserves, an increased focus on renewable energy and growing fuel demands an alternative is required. A potential solution to this is to use a small scale Fischer-Tropsch synthesis system to produce hydrocarbon fuels as part of a biomass to liquids process. This research investigated various cobalt catalyst formations and Fischer-Tropsch reactor designs to identify the most suitable combination to for a small scale system to convert 10 SL∙min-1 of synthesis gas to hydrocarbons. Catalysts were created using washcoating, electrochemical deposition and solution combustion synthesis methods and tested in one or both of the two reactor designs. The first reactor design utilised a 2 mm x 20 mm channel which held a catalyst support structure made from wire mesh or metal foam which also created microchannel type flow spaces. The second reactor design consisted of various numbers of 0.3-3 mm wide wire-cut microchannels in a thin stainless steel shim plate. Catalysts formed in the first reactor design using washcoating or solution combustion synthesis methods were found to agglomerate forming large particles which presented no detectable activity for the Fischer-Tropsch synthesis. Forming the catalysts for this reactor ex-situ using electrochemical deposition was successful in producing fine microstructures of catalyst which were initially active for the reaction. This activity did not last however with a complete loss after a few hours on stream. Using the microchannel reactor design, the results were much more successful. Micro-structured catalysts were able to be created using both the washcoating and solution combustion synthesis methods. However for wider channels only the solution combustion synthesis method could produce suitable catalysts with 0.9 mm found to be the optimum channel width. The solution combustion synthesis catalyst achieved a higher average CO conversions of 40±2% than the washcoat (20±3%) when run in Fischer-Tropsch synthesis conditions. Analysing the hydrocarbon product from the solution combustion synthesis catalyst run yielded an ASF α value of 0.795 and a C5+ selectivity of 73% which are very comparable to the literature. This combination was utilised to design a larger system which with the addition of a heat exchange system can be scaled up to run in the biomass to liquids system.