Pyrolytic assessment of the recalcitrance of hydrothermal carbonization products from eucalypt sawdust as an index of its performance for atmospheric CO2 sequestration

Abstract

The hydrothermal carbonization basically consists of a thermal treatment of biomass mixed with water, in a closed vessel at relatively low temperatures (< 250 ºC). Under these conditions, the chemical structure of biomass is heavily transformed, via dehydration, condensation and aromatization processes. As a result, the obtained solid product (here denoted as hydrochar) exhibits higher percentages of carbon (C ~ 70%) in relation to the biomass (C ~ 50%) and abundant oxygen functional groups (typical O/C atomic ratio ~ 0.2–0.4) [1]. The carbon in the hydrochar product is believed to consist mainly of aromatic ring structures [2]. Our hypothesis is that hydrothermal carbonization of biomass may constitute a way to transform the biodegradable biomass carbon into nonbiodegradable carbon, thus representing an efficient way to sequestrate atmospheric CO2.