This paper focuses on the experimental demonstration of a three-stage GST (gas switching technology) process (fuel, steam/CO2, and air stages) for syngas production from methane in the fuel stage and H2/CO production in the steam/CO2 stage using a lanthanum-based oxygen carrier (La0.85Sr0.15Fe0.95Al0.05O3). Experiments were performed at temperatures between 750-950 °C and pressures up to 5 bar. The results show that the oxygen carrier exhibits high selectivity to oxidizing methane to syngas at the fuel stage with improved process performance with increasing temperature although carbon deposition could not be avoided. Co-feeding CO2 with CH4 at the fuel stage reduced carbon deposition significantly, thus reducing the syngas H2/CO molar ratio from 3.75 to 1 (at CO2/CH4 ratio of 1 at 950 °C and 1 bar). The reduced carbon deposition has maximized the purity of the H2 produced in the consecutive steam stage thus increasing the process attractiveness for the combined production of syngas and pure hydrogen. Interestingly, the cofeeding of CO2 with CH4 at the fuel stage showed a stable syngas production over 12 hours continuously and maintained the H2/CO ratio at almost unity, suggesting that the oxygen carrier was exposed to simultaneous partial oxidation of CH4 with the lattice oxygen which was restored instantly by the incoming CO2. Furthermore, the addition of steam to the fuel stage could tune up the H2/CO ratio beyond 3 without carbon deposition at H2O/CH4 ratio of 1 at 950 °C and 1 bar; making the syngas from gas switching partial oxidation suitable for different downstream processes, for example, gas-to-liquid processes. The process was also demonstrated at higher pressures with over 70% fuel conversion achieved at 5 bar and 950 °C.
© 2021 The Authors. Published by American Chemical Society.