Carbonization process of Moso bamboo (Phyllostachys pubescens) charcoal and its governing thermodynamics

The effect of a three-stage carbonization and activation process on the properties of a bamboo charcoal (BC), prepared from the 4- to 6-year-old Moso bamboo (Phyllostachys pubescens) planted in the Jhu-Shan of Nantou, Taiwan, was investigated. A process simulation, based on first principles thermodynamics, was conducted using a thermochemistry software package (FactSage). Our model not only reproduced the key experiments well, but also provided a detailed chemical reaction mechanism of the carbonization process involving multiple solids and multi-component gas phases. Three-stage process proposed herein consisted of first-stage carbonization process to prepare BC, second-stage activation process to activate BC, and third-stage activation process to refine activated BC. Measured changes in pH values of the BC were explained based on the chemistry of the gas products, and, accordingly, a theoretical maximum pH value for the BC was proposed. Furthermore, material properties like charcoal yield, ash content, pH level, elemental compositions, Brunauer–Emmett–Teller (BET) specific surface area, morphology, and Fourier transform infrared spectrum were measured. Interestingly, the observed maximum BET specific surface area (493.0 m2 g−1) of refined BC obtained through the above three-stage process was more than 2000 times larger than that of the sample fabricated at 400 °C in the first-stage carbonization process (0.2 m2 g−1), and this once again demonstrated the importance of process optimization. Our multi-stage process and new chemical reaction mechanism can be used to speed up the technology development of a general carbonization for a variety of bio-resources.