Microwave-assisted rapid pyrolysis of woodblock without adding susceptor and detailed product analysis

Microwave-assisted pyrolysis of cylindrical woodblocks (dia.~50–60 mm, height; 50–60 mm; weight: 50–70 g) has been performed to understand the effect of microwave distribution, microwave power, and final temperature on the product yields and bio-oil composition. Importantly, the microwave pyrolysis of woodblock without the addition of any external microwave absorber is demonstrated. Experiments conducted in a domestic microwave oven resulted in non-uniform pyrolysis of the woodblock due to the non-uniform distribution of microwaves. In contrast, uniform pyrolysis was observed in a research-grade microwave reactor equipped with an antenna. High reaction temperatures (600–700 °C) were achieved even with low microwave powers (220 W), indicating effective microwave conversion to heat energy by the woodblock. The bio-oil, bio-char, and gases yields were 47±2 wt%, 27±3 wt%, and 27±3wt%, respectively, and consistent at different microwave powers and reaction temperatures. However, a low yield of non-condensable gas and a high yield of biochar were observed at low microwave power (220 W) and 600 °C. The gas chromatography-mass spectroscopic (GC/MS) analysis revealed that bio-oil is a mixture of aromatics, syringols, guaiacols, simple phenols, furans, and others, and the composition of bio-oil was sensitive to the operating conditions. High selectivity to total phenolics, including syringols, guaiacols, and simple phenols, was observed to be 69% produced at 550 W and 600 °C. CO 2 and CO were the major non-condensable gases (35–45%), while H 2 was produced at 10–15%. High energy recovery in bio-char (~51%) was observed, proving that it can be used as a potential feedstock for gasification.