Sustainable Energy from Biogas Reforming in a Microwave Discharge Reactor

Abstract Biogas is one of the most important renewable energy sources in modern societies. Generated from livestock manure and industrial wastewater, it can provide considerable savings in energy costs and reducing environmental impacts. Thailand is reported to have the potential to produce over one billion m 3 of biogas a year. The biogas is generally utilized for heating, mechanical shaft works, and electricity generation. If pipeline networks or purification and compression facilities are not available, use of biogas is normally limited to only within and around farm areas. Alternatively, biogas may be converted via reforming reactions into synthetic gas. Because of presence of sulphur compounds in biogas, a catalytic reformer may face serious poisoning problem. In this work, non-catalytic, plasma assisted reforming of biogas was carried out at atmospheric pressure and room temperature in an 800 W, laboratory microwave discharge reactor. Effects of CH 4 /CO 2 ratio (1, 2.33, 9), feed flow rate (8.33 – 50 cm 3 /s), and oxygen addition in terms of CH 4 /O 2 ratio (1, 1.5, 2) on reactor performance (yield, selectivity, conversion, H 2 /CO and energy consumption) was investigated. It was found that biogas was successfully reformed into synthetic gas by a microwave plasma reactor under room temperature and non-catalytic conditions. For dry reforming of biogas, high H 2 and CO yields were obtained at low energy consumption. Presence of oxygen enabled partial oxidation reforming that produced higher CH 4 conversion, compared to purely dry reforming process. By varying CH 4 /CO 2 as well as CH 4 /O 2 ratios, synthetic gas with a wide range of H 2 /CO ratios can be generated. From the findings, it was suggested that the microwave plasma reactor may be practically used to reform biogas to produce more valuable intermediates or products such as synthetic gas.