3.1. Methane conversion
The distributions of methane conversion and the maximum
temperature with respect to the CO2/O2 ratio at O/C = 1 are
displayed in Fig. 3. The methane conversion is defined by
methane conversionð%Þ ¼
FCH4; in FCH4; out
FCH4; in
100 (9)
where FCH4; in and FCH4; out denote the molar flow rates of methane
at the inlet and the outlet of the reactor, respectively. Fig. 3a shows
that the slight addition of CO2 facilitates the methane conversion a
bit. Specifically, when the CO2/O2 ratio increases from 0 to 0.2, the
methane conversion is promoted from 60.3 to 60.6%. This arises
from the fact that the addition of CO2 is conducive to the forward
reaction of dry reforming (i.e. Eq. (4)). Once the CO2/O2 ratio is
larger than 0.2, however, the methane conversion is descending
with increasing the ratio. Fig. 3b depicts that the higher the CO2/O2
ratio, the lower the maximum temperature in the catalyst bed. This
can be explained by the shorter residence time of the reactants in
the catalyst bed. Besides, the concentrations of methane and
oxygen are reduced when more CO2 is added, thereby diminishing
the strength of methane combustion. Overall, the methane
conversion at O/C = 1 is between 58.3 and 60.7% within the