Hydrothermal Carbonization of Lignocellulosic Biomass: Kinetics and Pelletization Study

Hydrothermal carbonization (HTC) is a promising technology to convert diverse feedstocks to homogeneous energy-dense solid fuel. The resulting HTC solid fuel has favorable properties such as high energy content, low volatiles content, friability and hydrophobicity. Currently, kinetics of hydrothermal carbonization is not available for performing techno-economic analysis of hydrothermal carbonization process. In this study, a specially-designed two-chamber reactor was used to perform hydrothermal carbonization of lignocellulosic biomass. The hydrothermal carbonization of loblolly pine was performed at various conditions (e.g. HTC temperature, reaction times, and biomass particle size). The decreasing mass yield and increasing fuel density occurred at the first 1- 2 minute of the reaction. The simple reaction mechanism of two parallel first-order reactions was validated, and kinetic parameters were presented. In addition, the excellent properties of HTC pellets were identified like forming robust pellets, stability in water, high volumetric energy density, as well as the ease of pelletization without adding any binder. Hence, this study pointed out hydrothermal carbonization process could help greatly overcome technical and economic barriers in thermochemical conversion of lignocellulosic biomass for fuels, chemicals, and electricity.