Optimization of pyrolytic oil production from coconut shells by microwave-assisted pyrolysis using activated carbon as a microwave absorber

Coconut shell waste pollutes the environment and affects public health. Converting coconut shell waste to pyrolytic oil (liquid smoke) with antimicrobial properties using microwave-assisted pyrolysis and activated charcoal as an absorbent is a promising solution. The purpose of this study is to investigate the process factors involved in the manufacture of coconut shell pyrolytic oil (liquid smoke) using microwave-assisted pyrolysis, to identify the chemical components in coconut shell pyrolytic oil, and to optimize the process factors using a face-centered central composite design (FCCD). This study further used coconut shells of various sizes (1-3 mm) and employed microwave-assisted pyrolysis with different power levels (300-600 W) and pyrolysis times (5-30 min). The results revealed that the pyrolytic oil (liquid smoke) yield increased as the time and microwave power increased but decreased as the size of the materials decreased. The optimum yield obtained was 34.6% at the following conditions: power of 593.6 W, material size of 2.9 mm, and heating time of 28.5 min. The analysis of the components of the volatile compounds in the pyrolytic oil (liquid smoke) product obtained from gas chromatography-mass spectrometry (GC-MS) analysis identified a total of 14 chemical components in coconut shell pyrolytic oil (liquid smoke) at 300 W, 15 compounds at 450 W, and only 5 components at 600 W. Among these compounds, phenol, dimethoxy phenol, guaiacol, hydroxyanisole, and methoxyphenol were found to have the highest concentrations. The outcomes of this study offer valuable contributions to the development of pyrolytic oil (liquid smoke) products with enhanced quality, flavor, and potential applications in the food industry.