Experimental and thermodynamic studies of the catalytic partial oxidation of model biogas using a plasma-assisted gliding arc reactor

The present work is an investigation of the influence of process conditions on the production of synthesis gas (H2 and CO) from model biogas (molar ratio of CH4/CO2 = 60/40) through partial oxidation over a granular Ni-based catalyst. The investigations were performed in a partially adiabatic plasma-assisted (non-thermal) Gliding Arc (GlidArc) reactor in a transitional flow regime at a fixed pressure (1 bar) and electric power (0.3 kW). The emphasis of this investigation was on an experimental study and a comparative thermodynamic analysis. The equilibrium compositions were calculated using a Lagrange multiplier and resulted in the development of systems of non-linear algebraic equations, which were solved numerically using the MATLAB® function “fmincon”. Two cases were studied: normal air (molar ratio of O2/N2 = 21/79) and enriched air (O2/N2 = 40/60). The individual effects of the O2/CH4 molar ratio and the bed exit temperature (Texit) were studied in both cases. The main trends of the CH4 conversion, the synthesis gas yield, the H2/CO ratio and the thermal efficiency of the reactor were analyzed, and it was shown that any deviations from equilibrium could be explained by temperature gradients and irregular gas flows. The results of this study revealed that CO2 could be used as a neutral gas in this process. When normal air was used, an O2/CH4 molar ratio of 0.66, a gas hour space velocity (GHSV) of 1.26 NL/gcat/h, a maximal temperature (Tmax) of 870 °C and an exit temperature (Texit) of 630 °C were found to be optimal parameters, and when enriched air was used, these ideal parameters were an O2/CH4 molar ratio of 0.64, a GHSV of 0.86 NL/gcat/h, a Tmax of 860 °C and a Texit of 635 °C.

► Plasma-assisted GlidArc reactor for catalytic partial oxidation of model biogas.
► Normal air (O2/N2 = 21/79) and enriched air (O2/N2 = 40/60) are used.
► Synthesis gas (H2 + CO) production by experimental work followed by comparative thermodynamic analysis.
► Deviations from equilibrium are explained by temperature gradients and irregular gas flows.