Characteristics optimization of empty fruit bunches chars using central composite design

The oil palm industry produces wastes that have not been used optimally and may cause pollution to the environment. This study used oil palm empty fruit bunches (OPEFB) to produce char using hydrothermal carbonization (HTC) process, the char might be used as pollution absorbent hence add its economic value. This research aims to evaluate the hydrochar characteristics and to determine the optimum temperature and reaction time of HTC process. Response surface methodology (RSM) coupled with central composite faced-centered design (CCF-CD) was used to optimize the experimental factors. The process used temperature of 130–170 °C for 3–5 h of reaction time. The hydrochar and raw OPEFB characterization have been performed to determine elemental and proximate analysis, iodine number, surface area, function group changes, decomposed compounds, and thermal characteristics. The results showed that the HTC process caused the decomposition of hemicellulose, cellulose, and a little of lignin. On the other hand, the surface area and fixed carbon of hydrochars were higher than the raw OPEFB. The optimum condition for the HTC process involving the yield, fixed carbon, and iodine number was at 160.38 °C for 3 h. The prediction of three responses based on the optimal condition was 82.804 to 84.052% for yield, 239.66 to 265.16 mg/g for iodine number, and 45.906 to 47.054% for fixed carbon. The results indicated that this HTC process might be applied for other lignocellulosic wastes to produce char that can be used as pollutant adsorbent.