Elaeis guineensis leaves for potential renewable sub-bituminous coal: Optimization of biochar yield by response surface methodology and product characterization

Pyrolysis of oil palm biomass residue can convert the rich organic matter in biomass into sustainable green energy, thereby addressing the challenge of surplus oil palm biomass residue generated during cultivation. Nonetheless, the pyrolysis of oil palm leaves (OPLs) has received limited attention. In this study, design of experiment-response surface methodology (DoE-RSM) was employed to identify the optimal combination of reaction temperature, residence duration, and nitrogen (N-2) flow rate for maximum biochar yield. The elemental analysis, high heating value (HHV), functional group, morphology, pore structure, and thermal behavior were assessed. By varying the operational parameters using response surface methodology, the biochar yield increased by 32.6-85.3%. The DoE-RSM predicted a theoretical yield of 52.1% at 344 degrees C, 146 min, and 3.2 scfh N-2 flow rate. The experiment confirmed a comparable yield of 53.7% at the stated parameters. The HHV of 24.14 MJ kg(-1) was recorded under optimal conditions, and was comparable to sub-bituminous and bituminous coal. Fourier transform infrared analysis validated the OPL biochar by weakening O-H, C=O, C-OH, and C-H peaks. Scanning electron microscopy images revealed enlarged pores and altered morphology in the OPL biochar. X-ray diffraction showed lower crystallinity of the OPL biochar than the feedstock. Raman spectroscopy showed higher I-D/I-G, indicating a more disordered carbon structure in the OPL biochar. Thermogravimetric analysis confirmed higher temperature for main devolatilization of OPL biochar, and the differential thermogravimetric analysis curve pattern resembled that of Mukah Balingan coal. The findings are helpful for an initiative to convert a large amount of leftover OPLs produced during cultivation and to turn them into high value-added material for a sustainable contribution to a circular carbon economy. (c) 2023 Society of Industrial Chemistry and John Wiley & Sons Ltd.