AbstractOriginal data for mass, element, and methane dynamics under controlled pyrolysis are presented for several biomass feedstocks. The experimental system consisted of an environmental (low-vacuum) scanning electron microscopy (ESEM) with a hot-stage and energy-dispersive X-ray spectroscopy (EDS) detector. A tunable diode laser (TDL) was coupled to the ESEM vacuum pump to measure the methane partial pressure in the exhaust gases. Thermogravimetric analysis and differential thermal analysis (TG/DTA) in a N2 atmosphere was also carried out to assess the thermal properties of each biomass. It was found that biochars were depleted or enriched in specific elements, with distinct methane formation change. Results depended on the nature of the biomass, in particular the relative proportion of lignocellulosic materials, complex organic compounds, and ash. As final temperature was increased, N generally decreased by 30 to 100%, C increased by 20 to 50% for biomass rich in lignocellulose, and P, Mg, and Ca increased for ash-rich biomass. Methane formation also allows discriminating structural composition, providing fingerprints of each biomass. Biomass with low ashes and high lignin contents peaks CH4 production at 330 and 460 °C, whereas those biomasses with high ashes and low lignin peaks CH4 production at 330 and/or 400 °C.