(507g) Significance of Oxygen Functional Groups on Pelletization of Hydrochar

Hydrothermal Carbonization (HTC) is an emerging thermochemical process to convert waste biomass into carbon-rich hydrochar in the presence of subcritical water. Previous studies have attempted to reach the overarching goal of HTC of lignocellulosic biomass to enhance the energy and mass densities by pelletization of hydrochars. It has also been revealed that hydrochars unlike torrefied or pyrolysis biochars, contains significantly higher amount oxygen functional groups on the surface. In this study, the main hypothesis is oxygen functional groups enhance mass and energy density of hydrochar during pelletization. In order to prove the hypothesis, Boehm titration and back titration were performed to quantify acidic oxygen functional groups (acetic, lactonic, and phenolic) and basic functional groups of hydrochars, respectively. Rest of the oxygen functional groups are evaluated by relative transmittance area percentage (RTAP) from Fourier transform infrared spectroscopy (FTIR) spectra of the hydrochars. In this study, hydrochars were prepared from corn stover and loblolly pine at three different HTC temperatures (200, 230, and 260°C) and 30 min or reaction times. Pelletization of hydrochars were performed in a single press pellet press with varying pelletizing pressures and pelletization temperatures. Scanning Electron Microscope (SEM) at lower and higher magnification was done to analyze the internal surface morphology on the transverse plane of the raw and hydrochar pellets. It was found that acidic oxygen functional groups on hydrochar increase with the increase of HTC temperature and hydrochar pellet’s mass and energy density are also increased with the HTC temperatures. Moreover, the acidic oxygen functional groups enhance the inter-particle bindings of the hydrochar particles at higher pelletization temperatures and higher pelletization pressures, which resulted in lower crack densities on the hydrochar pellets.