Dipl. Ing. Matthias Mayerhofer Technische Universität München ...

Abstract I
Abstract
The effectiveness of three different catalysts regarding tar cracking and decomposition of syngas
deriving biomass gasification in a fluidized bed has been investigated in this study. The catalysts
that were tested were iron based, and commercially available nickel based and precious metal
catalysts in order to compare their ability to decrease the amount of tar in the product gas. The
catalysts were tested in different temperatures and residence times. The reference operating conditions
were 800°C and a space velocity of 6500 1/h. The nickel based catalysts were proved to be
the most effective by achieving conversion of ~99%, precious metal ~97% and iron based catalysts
~40%. The contribution of the thermal destruction was evident for the iron based catalysts; when
the temperature was raised to the highest point (860°C) the conversion rose to ~70%. The blank
experiment indicated that the contribution of the temperature is ~12% of conversion. For the iron
based catalysts, some compounds such as naphthalene increased in the product gas, which indicates
the stability of its molecule. However, when the temperature got higher, the only compound
that didn’t decrease was biphenyl. The iron and nickel based catalysts were stable, and no sign of
deactivation was observed during the tests. As for the precious metal catalysts, the CH4 in the
product gas after the catalytic bed was initially ~0%, but gradually rose to ~5% and stabilized at this
value. This could possibly indicate deactivation of the catalyst in the beginning, but it reached stability
soon and remained in stable state during the whole experiment. The characterization of the
iron based catalysts was realized before and after the tests to define the influence of the steam
reforming on its surface (X-Ray Diffraction, BET surface measurement, SEM). The BET measurement
of the iron material revealed that the active sites of the catalysts were reduced after its use,
although that didn’t affect its effectiveness regarding tar decomposition. The iron based catalysts
need optimization in their structure. The particles were fine and soft, so they were blown away during
the experiment. Possible evolution of their material could achieve higher tar conversion, particle
strength and render them a feasible material for in situ use.
Key Words: Iron based catalysts, nickel based catalysts, precious metal catalysts, tar removal,
biomass gasification