(601f) Catalytic Performance of Supported Nano-Iron Catalysts Synthesized By a Gas-Expanded Liquid Deposition Technique in Fischer-Tropsch Synthesis
AIChE Annual Meeting
Wednesday, November 16, 2016 - 4:55pm to 5:15pm
In this study, a new catalyst was prepared using pre-synthesized iron oxide nanoparticles that were controllably deposited onto a SiO2 support using a gas-expanded liquid precipitation technique (GXL).Â In general, gas expanded liquids are solvent systemsâ??typically a mixture of an organic solvent and a compressible gas, such as CO2â??that enable controlled deposition of pre-synthesized nanoparticles, based on their size, onto a support surface.Â By controlling the applied CO2 pressure, and hence the solvent strength, one can systematically deposit/precipitate nanoparticles of desired sizes onto the support materials. The iron oxide nanoparticle dispersion used in this study contains oleic acid stabilized iron oxide nanoparticles dispersed in an n-hexane solvent. We induced the precipitation of larger sized particles from the initial nanoparticle dispersion, thereby depositing these larger particles onto the surface of the support while enabling the removal of the smaller sized particles by removal of the residual hexane solution. The ability to exclude the smaller sized particles from those that are deposited onto the catalyst support is important since supported iron FT catalysts with nanoparticles of small size have lower activity due to their stronger interaction with the support surface. As an added benefit, the lower viscosity and higher mass transfer coefficient in the GXL can enhance the diffusivity of the iron particles into the catalyst pores during deposition, resulting in a more uniform distribution of the nanoparticles compared to traditional methods.
The objective of this work is to explore the benefits of using the GXL technique in preparing SiO2 supported catalysts with moderate iron loadings for Fischer-Tropsch synthesis applications. The catalytic performance of GXL prepared Fe/SiO2 catalysts with different iron loadings were evaluated in terms of CO conversion, CH4 selectivity, C5+ selectivity and C5+ productivity. In addition to the effect of iron loading, we have also investigated the effect of reaction conditions, such as reaction temperature, on the catalytic performance of our GXL catalysts in order to understand the influence of operating conditions on the selectivity and productivity of desired hydrocarbon products.