Production of solid biofuel from agricultural wastes of the palm oil industry by hydrothermal treatment

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.