In this study, upgrading of agricultural waste, in the form of oil palm fronds and trunks, into solid biofuel was investigated using hydrothermal treatment. A slurry of 300 mL of water and 30 g of material was treated in a 500-mL batch autoclave equipped with stirrer, thermometer, and pressure sensor. Experiments were conducted in the temperature range 200-350°C at an initial pressure of 2.0 MPa. The slurry was gradually heated to the target temperature and held for a further 30 min. Approximately 35-65% of the original material was recovered as a solid product with favorable solid fuel characteristics. The gross calorific value ranged from 19.9 to 29.7 MJ/kg and the equilibrium moisture content was 7.6-4.5 wt%. The carbon content varied from 51.4 to 78.5 wt% and the oxygen content was 42.1-16.1 wt% after upgrading. Changes in the solid composition and carbon functional groups following upgrading were identified by FTIR and 13C NMR. In addition, analyses on the liquid product (by GC-MS) and the gas product (by GC) were carried out to clarify the decomposition behavior of material.
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