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

Abstract

The present work is an investigation of the influence of process conditions on the production of synthesis gas (H 2 and CO) from model biogas (molar ratio of CH 4/CO 2 = 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 O 2/N 2 = 21/79) and enriched air (O 2/N 2 = 40/60). The individual effects of the O 2/CH 4 molar ratio and the bed exit temperature (T exit) were studied in both cases. The main trends of the CH 4 conversion, the synthesis gas yield, the H 2/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 CO 2 could be used as a neutral gas in this process. When normal air was used, an O 2/CH 4 molar ratio of 0.66, a gas hour space velocity (GHSV) of 1.26 NL/g cat/h, a maximal temperature (T max) of 870 °C and an exit temperature (T exit) of 630 °C were found to be optimal parameters, and when enriched air was used, these ideal parameters were an O 2/CH 4 molar ratio of 0.64, a GHSV of 0.86 NL/g cat/h, a T max of 860 °C and a T exit of 635 °C.