(265c) Effects of Biomass Contaminants (N and Cl species) On Fischer Tropsch Synthesis

The production of transportation fuels from biomass, and the use of biomass as a means of carbon dioxide capture and sequestration have been identified as a strategy with potential to address the energy and environmental concerns, including fuel independence, energy availability and reliability, and environmental issues, especially as related to global warming. Most of the contaminants are reduced to an acceptable level by the current coal cleaning processes, i.e. gas scrubbing process. However, the remaining impurities in biomass derived syngas may still negatively affect Fischer Tropsch synthesis catalysts with time on stream, which have not been fully comprehended and present many contradictions. This study has established an understanding of the influence of biomass-derived synthesis gas on the processes involved in syngas conversion to transportation fuels or chemicals.

Materials and Methods

Iron based catalyst containing K and Cu promoters on SiO₂ has been tested for the Fischer Tropsch synthesis using in a 1-liter Continuous Stirred Tank Reactor (CSTR) system. The contaminants in the simulated biomass syngas include nitrogen, and chlorine. The gas products were analyzed by an online micro-GC (Aglient 300A) and liquid/wax samples were analyzed by GC-MS (HP GC 6890, and HP MS 5973).

Results and Discussion

The ex situ contaminated Fe catalyst by NH₃ and HCl at 300 °C have been characterized using XRD, TPR, and XPS. Preliminary experiment results from XRD indicated that iron carbides were bulk materials after carburized in CO and then subsequently exposed to NH₃. However, predominant FeCl₂ were formed after CO carburization then followed HCl exposure. XPS results also indicated strong binding between Cl species and Fe at catalyst surface.  It is also interesting to find that after exposed to NH₄Cl in FT synthesis, the performance of Fe catalyst improved instead of deactivated. Areas of research to ensure the success of biomass conversion in presence of impurities include an understanding of the deactivation mechanism over the catalyst, and the identification of new catalyst materials through experimental and computational exploration.