Hydrothermal carbonization (HTC) is known as a thermochemical converting of wet biomass into a coal-like solid fuel (hydrochar). Hydrochar is easily crumbled. Because of hydrophobic properties, hydrochar is difficult to degrade by microorganisms. It has a calorific value comparable to lignite coal. In this study, hydrochar was made via converting the organic fraction of municipal solid waste through HTC at 190, 210, and 230°C for 30 min with feed to water ratio (FWR) 0.1, 0.2, 0.3. The feedstock processed includes food waste, paper, and wood waste, represented as a pseudo-component of the organic fraction of MSW. The high heating value (HHV), FTIR, as well as proximate and ultimate analyses were applied both to feedstock and hydrochar. The results showed that the energy density of hydrochar was elevated with increasing HTC temperature. The energy densification ratio and heating value increased by approximately 1.0–1.32 and 30%, respectively compared to raw feedstock. The lower yields of hydrochar were obtained at higher temperature. The typical char yields for lignocellulosic material range between 62–63 wt% at 190 °C and reduce to 54–57 wt% at 230 °C. Furthermore, a preliminary study of kinetic model for lignocellulose decomposition was conducted. This model was based on the mass loss rate of the lignocellulose compound in HTC of MSW. Three first-order reactions were given to illustrate the hydrochar yield at of 190, 210, and 230°C. The activation energy of lignocellulose decomposition was 76.26 kJ/mol, 51.86 kJ/mol, 12,23 kJ/mol for lignin, cellulose, and hemicellulose decomposition, respectively.
Albizia Chinensis is a plant easily found in Indonesia and other South East Asian countries. The sawdust from this plant is a lignocellulosic waste that can be potentially upgraded for the fuel purposes. This research investigated the potential of upgrading sawdust into a coal-like solid for fuel by a wet torrefaction process. In this project, a 1 L torrefaction reactor with an electric heater was employed to perform the carbonization of the Albizia chinensis sawdust. Wet torrefaction was performed in batch at temperatures of 190–230°C with holding times of 20°C, 30 and 60 min. The solid to water ratios of 1:3, 1:5 and 1:10 were used. The results showed that the chemical and physical properties of sawdust and hydrochar varied as a function of reaction temperature, holding time and solid load. The results also suggested that wet torrefaction could increase the fixed carbon in sawdust while the ash content and volatile matter decreased. The high heating value of hydrochar was 24.55 MJ/kg higher than raw sawdust, 18 MJ/kg. CO2 was predominantly detected in the gas phase, reaching the of >90% CO2. The liquid products were identified as sugar and organic acid compounds, which may be desirable feedstock for biochemical production.
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