Hydrothermal carbonization of lignocellulosic agro-forest based biomass residues

Abstract

To increase the understanding of hydrothermal carbonization (HTC) of lignocellulosic biomass residues, four feedstocks: giant bamboo, coffee wood, eucalyptus, and coffee parchment, were studied. The effect of operating conditions on the products in terms of yield, composition and energy densification were quantified. Each feedstock was treated for 3 h at temperatures of 180, 200, 220 and 240 °C. For all samples, the higher heating value (HHV), fixed carbon content and energy density increased with increasing reaction severity, while volatile matter content and mass yield decreased. The HHV of hydrochar samples obtained at temperatures ≥220 °C were in the range of 24.6–29.2 MJ kg−1 and indicated the high potential of these materials for fuel applications. The mass yields varied in the range of 46.5–56.9%, with the exception for coffee parchment, where the lower values of 34.4–46.0% were obtained. The fixed carbon varied from 33.8% to 53.0%. The HTC liquor had pH values of 2.9–4.4 due to organic acids. The results were used to model and evaluate different industrial-scale HTC simulation cases. The overall efficiency was similar within all studied biomasses. The integration with a bio-fired power plant allows simplification of the process while also bringing efficiency gains. All studied biomasses appear to be suitable for energy and value-added products generation through HTC treatment. Coffee residues, which have received little research consideration previously, responded well.