Effects of Pyrolysis Temperature on Characteristics of Porosity in Biomass Chars

In this study, the influence of pyrolysis temperature (T) in the range of 200-900°C on the characteristics of porosity in biomass chars was investigated. The samples were characterized by N₂ isothermal adsorption/desorption method and scanning electron microscopy (SEM). The results indicated that pyrolysis temperature had a notable impact on the pore structure and morphology of biomass char. Between 200 and 500°C, the removal of a significant amount of volatile matter produced pore opening. Above 500°C, the loss of only a relatively small fraction of volatile matter caused the development of porosity and the occurrence of the structural shrinkage and pore narrowing. High temperature led to plastic deformation of particles resulting in smooth surfaces and large cavities. The surface area reached a maximum value at 500°C, and at higher temperatures, the specific area dropped significantly, probably due to thermal annealing. Char structural ordering was likely to be a mechanism for thermal annealing and thus for thermal deactivation.