Microwave-assisted pyrolysis of palm kernel shell: Optimization using response surface methodology (RSM)

In this study, response surface methodology (RSM) based on central composite rotatable design (CCRD) was applied to determine the optimum condition for pyrolysis of palm kernel shell (PKS) using microwave-assisted pyrolysis system. Three operating variables, namely reaction time (min), sample mass (g) and nitrogen gas flow rate (mL/min) with a total of 20 individual experiments were conducted to optimize the combination effects of the variables. RSM based upon CCRD can be applied to correlate the experimental microwave-assisted pyrolysis results, with regression coefficients of 96.6, 95.0, 96.4 and 99.2 for the calorific value, fixed carbon content, volatile matters content and yield percentage, respectively. This proved that the RSM based on CCRD is efficiently applicable for the pyrolysis study using microwave-assisted pyrolysis system. The predicted optimum conditions for the pyrolysis process was at 31.5 min for reaction time, 30 g for sample mass and 100 mL/min for nitrogen gas flow rate, resulting in calorific value, fixed carbon content, volatile matters content and yield percentage of 29.9 MJ/kg, 59.8 wt%, 36.4 wt% and 40.0 wt%, respectively. Thus, maximum production of PKS char, with low volatile matters content and high calorific value and fixed carbon content via microwave-assisted pyrolysis system can be optimized using RSM.

► Char from palm kernel shells was produced using microwave-assisted pyrolysis. ► Power levels proportionally affect maximum temperature, fixed carbon and calorific value. ► Volatile matter and solid fraction of char are inversely proportional with the microwave power. ► Response surface methodology (RSM) was used to optimize the char production. ► Increasing the reaction time produced high calorific value and fixed carbon content char.