In this study, three diverse biomass feedstocks (loblolly pine, manure, and sewage sludge) were hydrothermally carbonized (HTC) and torrefied at different reaction times and temperatures. Solid hydrochars and torrefied chars, as well as their corresponding raw feedstocks, were characterized by ultimate, proximate, ash, stable carbon isotope (δ13C), and stable nitrogen isotope analysis (δ15N). The main goal was to determine the change of δ13C and δ15N with different thermochemical treatments. In terms of elemental carbon, mass yield, fixed and volatile carbon concentrations, the torrefaction of pine at 300 °C and HTC at 260 °C showed similar characteristics. However, δ13C values can distinguish between the torrefied char and the hydrochar, e.g. HTC at 260 °C was shifted to δ13C values as low as -29.2‰ while torrefied char at 300 °C was shifted to approx. -27.4‰. Moreover, manure-derived and sludge-derived hydrochars showed distinct δ13C and δ15N characteristics vs. pine hydrochars. δ15N values show a dependency upon HTC reaction time, with a longer reaction time producing a larger positive shift vs. initial feedstock δ15N values, e.g. manure-derived hydrochar reacted at 220 °C is shifted by +1.5‰ after 5 min, but by +3.0‰ after 30 min.

Elemental and stable isotopes (C, N) analysis of thermochemically treated biomass-derived chars

254th National Meeting (2017)

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