Combined Syngas and Hydrogen Production using Gas Switching Technology

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 (La_0.85Sr_0.15Fe_0.95Al_0.05O₃). 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.