Chemical looping tar reforming using La/Sr/Fe-containing mixed oxides supported on ZrO2
Graphical abstract
Section snippets
Introduction and background
Gasification of biomass presents a promising route to generate carbon-neutral synthesis gas (CO + H2), which can then be further processed into valuable gaseous and liquid fuels such as Substitute Natural Gas (SNG), Dimethyl Ether (DME) or others [1], [2], [3]. Apart from the desired major syngas compounds, raw gasification gas usually contains impurities and contaminants such as sulphur compounds, ammonia, non-condensable hydrocarbons and condensable hydrocarbons usually referred to as tars [4].
Experimental setup and procedure
Experiments were conducted in a small-scale fluidized bed reactor and the experimental setup is illustrated in Fig. 2. A detailed description of this experimental setup can be found in a previous publication [11]. Experiments were conducted with 9 g of bed material sieved to a size range of 125–250 μm. Additionally, empty reactor experiments were conducted to determine the extent of homogeneous gas phase reactions which could not be attributed to the bed material. To emulate the circulation of
Gas concentration profiles
In Fig. 3 the recorded gas concentration profiles are shown with ZTECH_LaSrFe as a bed material and 1.4 % C6H6 in the gasification gas at T = 800 °C. In the beginning, the fully oxidized bed material is exposed to gasification gas and thus reduced. It oxidizes the gasification gas, resulting in a peak in H2O and CO2 concentrations. Once these concentrations stabilize the material has reached its thermodynamically stable state and the bed material does not provide oxygen to the gas any longer.
Discussion
The results presented in Fig. 4 together with the results of the XRD analysis of the materials indicate that only the impregnation with La and Fe yields materials with a significant catalytic activity for benzene reforming; however this catalytic activity does not seem to require the existence of a crystalline La1-xSrxFeO3 phase, since the ZTECH_LaSrFe material exhibits high catalytic activity without such a phase being present during the experiment. The high catalytic activity could originate
Conclusions
In this study ZrO2-supported bed materials were investigated with respect to their tar removal capabilities in a chemical looping reforming system with benzene and ethylene as tar surrogates. ZrO2 was impregnated with individual metals La, Fe and Sr and combinations thereof corresponding to LaFeO3 and La0.8Sr0.2FeO3 perovskites, and it was found that only combinations of La and Fe yield significant conversion of benzene. The addition of Sr to La and Fe proved to be very beneficial for benzene
Acknowledgments
This work has been supported by the Swedish Gasification Center and the Chalmers Energy Area of Advance.
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