Microwave pyrolysis of food waste for high-quality syngas production: Positive effects of a CO2 reaction atmosphere and insights into the intrinsic reaction mechanisms

CO2 steam reformation technology for the conventional pyrolysis of food waste has been proven to effectively improve the bio-gas yield. However, the syngas proportion is low. This work systematically investigated the effects of a CO2 reaction atmosphere on the improvement of the syngas yield and the intrinsic reaction mechanisms during the microwave pyrolysis of food waste. The results show that an increased microwave power promoted the generation of bio-gas by rapidly increasing the pyrolysis temperature of the food waste. When the microwave power was 1400 W, the bio-gas yield in the CO2 reaction atmosphere reached 67.90 wt%, and the yield of the syngas in the bio-gas was 44.13% higher than that in the N-2 atmosphere (46.73 L/kg food waste). The concentrations of H-2, CH4, and CO in the bio-gas increased rapidly at temperatures between 200 degrees C and 600 degrees C. However, the concentrations of H-2 and CH4 gradually decreased as the pyrolysis temperature increased from 600 degrees C to 900 degrees C, which was caused by H2 and CH4 reacting with CO2 to form CO. In addition, the reaction of the light organic matter (e.g., aliphatic hydrocarbons and oxygen-containing compounds) in the bio-oil with CO2 was the critical process that improved the syngas yield. The content of polycyclic aromatic hydrocarbons decreased by 6.13% due to the inhibition of the aromatization reaction of the organic matter. Compared to the N-2 atmosphere, the CO2 atmosphere not only promoted the generation of CO from bio-char gasification but also significantly improved the specific surface area of the bio-char (from 143.66 m(2)/g to 205.71 m(2)/g), which provided the possibility for subsequent resource utilization.