Jeremiah Benoit1, Kanchan Mondal2, and Tomasz Wiltowski2. (1) Mechanical Engineering and Energy Processes, Southern Illinois University, Carbondale, IL 62901, (2) Department of Mechanical Engineering and Energy Processes, Southern Illinois University, Carbondale, IL 62901
The paper presents the results from research on conducting FT synthesis in supercritical CO2 from syngas typically produced from coal gasification and using a Fe-Zn-K catalyst. The data show and enhancement in the hydrocarbon selectivity and reduction in the parasitic loss of carbon efficiency due to carbon dioxide formation along with significant improvement in the conversion rates and an increase the life of the catalyst. This was achieved by employing a unique reactor setup that can conduct gas phase or supercritical phase FT synthesis in both batch or flow modes. The use of the supercritical CO2 (ScCO2) inhibited both methane and CO2 selectivities while enhancing the rates of synthesis and altering the Anderson Schulz Flory distribution by favoring the desorption of ƒÑƒ{olefins formed on the catalyst surface. In addition, the use of supercritical CO2 was found to prolong the life of the catalyst presumably by removing the heat of reaction from the catalysts surface and solubilizing the waxes that tend to deposit of the surface. Although not within the scope of this paper, the products from such a reactor system can be easily separated without the need of an additional unit process simply by tuning the pressure and temperature. The product spectrum and the selectivites for the different products will be presented. The effect of process parameters such as temperature, pressure, CO2 partial pressure on the product spectrum will also be presented. The clear increase in CO conversion at H2:CO ratio of 1:1 in supercritical phase as compared to gas phase reaction, the decrease in CO2 and CH4 selectivity, overall liquid product distribution finally an increase in the life of the catalysts as compared to gas phase synthesis clearly show the potential of the use of supercritical medium (ScCO2) for coal to liquid fuels conversion especially since the reactions can be conducted in a two phase regime without losing the benefits of the 3-phase slurry reactor systems.