(613f) Fate of Inorganics during Hydrothermal Carbonization of High Ash Fraction of Air Classified Biomass

Feedstock preparation and transportation are two major upstream challenges for any biorefinery. Biomass is often wet (>60% moisture), has low bulk density (60-300 kg m^-3) and contains high ash (1-25 wt%). High moisture and low density significantly limit the transportation and storage of biomass, while high inorganics, especially alkali and alkaline earth metals and phosphorus (AAEMs+P), promote scaling and fouling on heat transfer surfaces, and often catalyze to produce undesirable products. It has been shown that air classification can economically remove fractions of forest residues that have high ash content; however, however, a significant fraction of organics is removed as well.

The goal of this study was to reduce the AAEMs+P from the high ash fraction of air classified forest residues (AC-FR) using Hydrothermal Carbonization (HTC) because HTC has been proven effective for leaching monovalent and divalent cations as well as halides. Therefore, high ash fractions of AC-FR was subjected to HTC at temperatures of 180-260 °C. Solid hydrochars were characterized with induced coupled plasma (ICP), ultra violet visible spectroscopy (UVVIS), ultimate analysis, proximate analysis, and scanning electron microscopy-electron dispersive X-ray spectroscopy (SEM-EDS). Meanwhile, HTC process liquids were characterized ICP and UVVIS in order to perform mass balance of AAEMs+P. The results showed that AAEMs have leached from solid to liquid and a higher HTC temperature increases the leaching. It was also observed that higher HTC temperature reduces elemental carbon and oxygen from solid. Therefore, the overall ash content of hydrochar remains similar at higher HTC temperatures, despite of an overall reduction of AAEMs from solid.