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

Experiments 47
6.3.1Experimental Procedure
The two most important parameters that affect the tar conversion in a catalyst bed are the temperature
at which the catalyst operates and the residence time of the gas inside the bed. Therefore the
study for the iron based catalysts was made at three different temperatures 750°C, 800°C and
860°C to see how the behavior of the catalyst changes with the increase of the temperature. For
these series of experiments the space velocity was ~6500 1/h. In a second phase the temperature
was maintained at 800°C and the pressure drop varied at the values of 0.45 mbar, 0.9 mbar, 1.5
mbar, and 2.0 mbar to determine the tar conversion as the space velocity varied. The reason why
the temperature of 800°C was chosen in the second phase is because the future intention for the
iron based catalysts is to use them in situ as they don’t get easily deactivated by coke deposition.
Before each tar sampling the gas was left running through the catalyst bed for ~1 ½ hours to
achieve stable gas composition.
For the Nickel and the precious metal catalysts temperature of 800°C was kept as constant and the
space velocity was chosen for pressure drop 0.9 mbar and 2 mbar to have comparable operating
conditions with the iron based catalysts. In order to define the influence of the space velocity to the
gas composition for nickel catalysts, the dp was raised to 3.0mbar and 4.0mbar. As for the precious
metal catalysts, there was a sampling point of gas composition at dp=0.45 mbar.
All the catalysts were reduced 24 h prior to the experiments with a mixture of H2/N2 (10%/90%).
They were flushed with the forming gas while the temperature was being raised from room temperature
to 800°C. As for the iron and nickel catalysts, the H2 was reduced in the beginning as it reacted
with the oxygen from the catalyst’s surface. When the amount of H2 started to rise again,
then reduction of the catalyst was assumed. It is probable that the precious metal catalysts were
not in oxidizing state at the first place. However, the reduction procedure was applied for all the
three types to have one single pre-treatment procedure. In the following Figure 20 and Figure 21
the change of the monitored amount of H2, as a function of temperature is presented for both the
iron and nickel catalysts respectively.
10
9
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7
6
5
4
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2
1
0
H_2
0 200 400 600 800 1000
Temperature (°C)
Figure 20: Reduction of Iron based catalyst