Effect of hydrothermal carbonization temperature on pH, dissociation constants, and acidic functional groups on hydrochar from cellulose and wood

Abstract

The aims of this work were to quantify chemical states associated with the pH, dissociation constants, and pH at point of zero charge (pHPZC) of hydrochar and to quantify the acidic functional groups on hydrochar surface. Hydrochars from cellulose and wood treated at 180, 220, and 260 °C with 30 min residence time were produced. Boehm titration was applied to analyze acidic functional groups and dissociation constants on hydrochar surfaces. FTIR spectroscopy was used to identify the functional groups qualitatively. The results of this study indicate that hydrochar becomes more acidic due to a larger number of acidic functional groups on the hydrochar surface with the increase of hydrothermal carbonization (HTC) temperature. The total number of acidic functional groups increased from 20.5 ± 0.3 μmol/g to 1267.9 ± 22.5 μmol/g and 576.6 ± 7.8 μmol/g to 680.8 ± 18.8 μmol/g for cellulose and wood, respectively.