Uncovering the transition between hydrothermal carbonization and liquefaction using differential scanning calorimetry

Abstract

The in situ analysis of hydrothermal carbonization (HTC) and liquefaction (HTL) processes can be accomplished using high-pressure differential scanning calorimetry (DSC), a continuous, relatively inexpensive, and rapid technique for pressurized processes. A recently published DSC method is newly applied across conditions spanning both HTC and HTL to continuously assess the heat release profile of cellulose across the hydrothermal spectrum. The resulting DSC curves are deconvoluted and the peaks are assigned to reaction sets. HTC and HTL are both exothermic, with enthalpy changes of ~0.3–0.9 and ~0.9–1.2 kJ g−1 for HTC and HTL, respectively. A thermodynamic transition in overall process enthalpy occurs at the transition from HTC to HTL, which can be explained by the relative importance of hydrolysis, polymerization, and bulk carbonization reactions within the two processing regimes. This novel DSC technique could reduce cost and time in the initial evaluation of potential HTC and HTL feedstocks, which may hasten the commercialization of these thermochemical processes.