Enhancement of Biochar Gasification in Alkali Hydrothermal Medium by Passivation of Inorganic Components Using Ca(OH)2

Abstract

The challenges with thermal gasification of biomass to produce syngas include high transportation and drying costs of biomass and the need for high-temperature (700–1000 °C) gasifiers and conditioning of the produced gases. Some of these challenges can be addressed by first converting biomass into high-energy-density biochar before transportation and then hydrothermal gasification of biochar at the site of the Fischer–Tropsch plant for liquid fuel synthesis. In this work, a high-energy-density (>27 MJ/kg) biochar is first produced via hydrothermal carbonization of switchgrass at 300 °C, and then the biochar is gasified in hydrothermal medium at 400–650 °C. The carbon gasification efficiency in hydrothermal medium is much better than that in the thermal medium. For example, at 550 °C, only 5.9% carbon gasification was achieved in the thermal medium, as compared to 23.8% in hydrothermal medium. The addition of 25 wt % K2CO3 catalyst enhances the hydrothermal gasification to 43.8%. The gasification can be fu...