Valorisation of oil palm wastes into high yield and energy content biochars via slow pyrolysis: Multivariate process optimisation and combustion kinetic studies

Palm kernel shell (PKS) and empty fruit bunch (EFB) are agricultural wastes discharged in significant quantities by the Malaysia palm oil industry. In this work, valorisation of these wastes via slow pyrolysis were experimentally and statistically investigated to synthesise biochars. The interactive effects of several synthesis parameters (nitrogen flowrate, heating rate, pyrolysis temperature and time) on two pyrolysis process responses, viz biochar yield and higher heating value (HHV), were simultaneously assayed. The pyrolysis variables were optimised by response surface methodology (RSM) to maximise the two responses. It was determined that the optimum conditions for the biochars synthesis were 30 mL min⁻¹ flowrate, 18.9–20 °C min⁻¹ heating rate, 500–504.3 °C pyrolysis temperature and 30 min pyrolysis time. Under these synthesis conditions, the biochar yields were 34.27 and 36.86%, and HHV were 26.64 and 28.96 MJ kg⁻¹ for EFB-biochar and PKS-biochar, respectively. The proximate analysis revealed that the biochars exhibited high fixed carbon contents. The current study also demonstrated that the activation energies of the EFB-biochar and PKS-biochar were three times lower than their corresponding raw wastes signifying the importance of the developed biochars as promising feedstock for combustion and gasification applications.