White Poplar Microwave Pyrolysis: Heating Rate and Optimization of Biochar Yield

White poplar is an important biomass resource because of its high yield and fast-growing characteristics. Experiments were conducted to study the effects of microwave power, moisture content, and particle size on the heating rate and biochar yield. A Central Composite Design (CCD) was used to optimize the biochar yield. The CCD results showed that a maximum temperature-increasing rate of 2.71 °C/s was obtained with a microwave power of 2 kW and a small particle size of 100-mesh. High power, small size, and high moisture content would benefit the increase of the heating rate. An optimum biochar yield of 0.905 kg per kg poplar was obtained with a microwave power of 3 kW, moisture content of 1%, and temperature of 500 °C.