(449b) Molecular and Microkinetic Modeling of Catalytic Supercritical-Phase Fischer-Tropsch Synthesis

Asiaee, A., South Dakota School of Mines & Technology
Benjamin, K. M., South Dakota School of Mines and Technology

The use and advantage of supercritical fluids (SCFs) as solvents in heterogeneous catalysis has been explored in several systems, including supercritical water oxidation, green chemistry, hydrothermal biomass conversion (gasification and pyrolysis), and catalytic Fischer-Tropsch (FT) synthesis in supercritical hexane.  In the particular case of FT catalytic chemistry, the use of supercritical hexane has shown improved CO conversion and an improved product slate.  While there has been much experimental work in the area of heterogeneous catalysis in supercritical fluids, and in the development of SCF FT technology in particular, there is no current molecular-level understanding of the role(s) of the SCF during catalysis.

This work involves molecular and microkinetic modeling of catalytic SCF FT synthesis.  Density functional theory (DFT) calculations have been applied to model the kinetics and thermodynamics of Fischer-Tropsch synthesis reactions on a model Co(0 0 1) catalyst in presence of supercritical hexane. In this regard, by utilization of the DFT-GGA method, the important elementary reactions have been determined to find out the probable mechanisms and investigate the effect of pressure and supercritical solvent on these catalytic reaction pathways.  An existing microkinetic model in the literature has been modified to include these pressure and solvent effects of supercritical hexane on catalytic thermodynamics (chemisorption) and kinetics, using a combination of the aforementioned DFT calculations and equation of state calculations.  Finally, reactor product yields have been compared with experimental results reported in literature, and net rate and sensitivity analysis results from the model are presented and discussed.