Simulating Fischer-Tropsch synthesis phase behavior in nonconventional reaction media
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Our research team is currently working on the design of an advanced Fischer Tropsch synthesis (FTS) reactor technology to operate in both conventional reaction media (gas phase and liquid phase) as well as on non conventional media (near critical and supercritical phase). The latter has been considered to leverage certain advantages over the existing commercial reactor technologies (fixed-bed reactors and slurry reactors) while overcoming several of their limitations. These have been attributed to the unique characteristics of the supercritical fluids that combine liquid-like density and heat capacity with gas-like diffusivity and transportation properties. Furthermore, simple tuning of reaction temperature and pressure around the critical point of reaction mixture would facilitate the selective control of the hydrocarbon product distribution as we have demonstrated in a previous study. Nevertheless, design a reactor technology for such non-conventional media would require series of investigations on the phase behavior of the reaction mixture as well as the FTS kinetics in non conventional media since the introduction of the supercritical solvent shifts the problem from a classical catalytic reaction engineering process to one combined with a thermophysical puzzle. In this study we are reporting a summary of our activities in simulating the phase behavior of the supercritical FTS reaction mixture under variety compositions of reactant (syngas) + solvent (middle distillate hydrocarbons, represented by hexanes) utilizing ASPEN Plus. The selected mixtures mimic the feed stream to the reactor bed, typical mixtures inside the reactor bed, and the product stream at the reactor outlet. The preliminary report shows a comparison between the simulated phase behavior of the reactor inlet and the experimentally measured phase of the same mixtures as obtained from a variable volume view cell. Our findings showed that simple tuning of reaction temperature and pressure could result in measurable changes in the reaction mixture physical and transportation properties (e.g. density, viscosity, etc.), which could be used to explain several of the advantages reported on FTS reaction performance in near and supercritical conditions.
